I want to go backpacking with a couple friends, but I'm the only one of us with any experience, and I mostly day hike. I've only done a couple of backpacking trips. They've never backpacked, and only hiked occasionally.
I can only tell you what I do, when I am in this situation. It's tricky, and getting everyone to agree can be tough, but it works.
First, be the leader. Don't just suggest people bring x or y, make them. Assert control over the trip and make sure to keep it. Now that doesn't mean you have to be an ass hat, but you do need to "take charge". Make sure you it's clear that you're going and they are coming along. It's hard to describe, because I don't mean to suggest that you be overbearing. But for example, make sure that everyone checks their gear with you. Make sure that everyone checks their food with you.
When people want to split off from the group make sure they know to check with you. Make sure they have you check their tent (or whatever) before they sleep in it.
I know this seems silly, but your the one with experience. Be ready to suggest products and items that they will need to bring or buy. Be prepared to call the trip off if it's not going "your way" on a critical issue. Again, sounds bad. But if you say to bring drinking water, and someone is insisting they don't need to because you can just drink from the river, then you suggest that they get some kind of water purification system and they go "no, river water should be fine", you need to make the call and stop the trip.
Where to go
Next, choose a short trip. If it's their first time, then they may not be prepared for what hiking means. Specially if it's off trail. A 2-mile run on a track is a lot different then a 2-mile walk on a animal trail. I would suggest a 1 mile in, setup camp, 1 mile or less out arrangement. Yes, that means a lot of time at camp, but you don't want to be setting up a tent for the first time at dusk. And you really don't want to have to deal with muscle pain, back pain, sore feet, etc. on the way out. You want to leave them wanting more.
Before the trip
Third, have a planning day. Get everyone together for dinner or something and go over what the requirements are. Focus on shoes, packs, survival gear and food. Then, on the second half of planning day head to the stores. Get everything you don't have. Be ready to answer questions about weight, what is needed and what is nice to have. I usually have to remind people that why they want to take is what they will have to carry. That usually gets them to put down the big hibachi grill and choose something more reasonable.
Then head to the grocery store. Get the food you want to take. Of course focus on lightweight high-energy foods. Be ready to explain your choices. Keep it simple. Canned food, beef maybe, fruits, nuts, and grains. Even though you may be comfortable preparing a lavish meal over a camp fire, it takes practice that they don't have. So stick with foods that are easy to cook, or don't require cooking. Remember to keep weight in mind. 10 pounds of steak sounds good, but remind them they they will have to carry it, and the ice to keep it edible.
The day before the trip, have a packing day. Invite everyone over again, and have everyone help each other pack. Make sure you try to distribute weight. Even if it means mixing items. Women usually have to be stopped from bringing to many clothes. Men have a tendency to want to bring too many gadgets. Stick what you need to survive in one pile, and what you want to be comfortable in another. Make sure everyone has their "survival gear". (For example I think a first aid kit, some water purification tabs, a glow stick, a striker (fire starter), a compass, a knife, some rope, and toilet paper are survival gear). I would want everyone to carry that themselves. Yes, that means there 6 first aid kits. No one ever dies from too many bandages. (But again a small kit is all that's needed.) Then look at your comfort gear. Split it up so the weight is even. Get everyone into their pack, and have them walk around a bit and make sure they're ok with the weight and nothing is off-center.
Once at the start of the trip, go over some safety info. Point out the ranger stations. Make sure everyone knows which way to walk and how to tell. Set up plans for being separated - both for the daytime and the nighttime. Go over the very basics: don't leave food about, keep your tent closed, keep clothes in your tent. Don't drink "raw" water. Go over what to do if someone is injured. Give everyone a map of the area you're hiking in and point out landmarks. See that big rock. That's this spot on the map. See that hill over there, here it is on the map. The river, that's this line right here. If you get lost, then you sit still and wait one hour. If no one finds you by then, you want to walk towards the river and then follow the bank to the big hill. You will either come the camp site or the ranger station.
Picking a campsite is easy; just make sure it's by a nice big landmark. If you're in a place with assigned camp sites then even better.
Setting up camp make sure you get your spot set up first. If you're using a tent, get it up first. Then help the others with theirs if they ask. If it starts to get dark, it may be time to take charge again, but hopefully, you're with friends and you're not being an ass, so if they need help they will ask. In line with being a leader though, you make the call. If it looks like they're headed for a bad situation help them out. Better mad then dead (or injured, or sick).
While camping stay on top of safety issues. Even if it means being a pest. Remind everyone to keep their food and trash away for example. Specially if you're in an area with bears, cougars, etc. Make it a point to turn in early. By now everyone should be following your lead as far as "what needs doing" so take advantage of that and turn in early. A little extra sleep will go along way.
Fire, if they have had no experience, then you just manage the fire. Again it can really depend on where you are, but if you're in a "dry" area, it doesn't take much for a bad fire pit to become a dangerous situation. Last think you want is the rangers showing up because someone got silly with the fat wood. Give lessons, show the differences, but make sure they at least check with you before adding to the fire. It takes a while to know if a log will burn for an hour or all night. If you need more heat to cook or if you just need to wait for more of the wood to burn.
I know it's gonna be weird, but when you stop for the night, and in the morning before you pack up, make sure to do a medical check. Most importantly, make everyone take their shoes and socks off and check for blisters or irritations. These nasty little suckers can turn a 1 mile hike into a hospital trip, and because there seem only minor, people tend to just "tough it out", when all they really need to do is make someone aware of it, and put on a bandage (when it's early). Same is true for rubbing of pants and pack straps (though just ask don't look). If you catch it when its "itchy", a little water and a bandage will take care of it. If they wait till it's bleeding and hurts to walk....
It seems silly, but when setting up camp, when on site, and during your planning meeting make sure to go over it. Different parks have different rules. There not always intuitive or pleasant.
I know I talk a lot about you taking charge. But this trip is supposed to be fun. Keep it fun. Taking charge doesn't mean being bossy. But it does mean taking responsibility for the situation. Make sure it's fun and not just a day of you bossing everyone around. Help when needed, interject when needed, but mostly just chill and get back to nature.
Make the trip short and easy. Better to have them wishing for something longer than regretting that they're stuck on the trail. Just spend one night on the trail, in good weather if you can arrange it. The four most important things for comfort are sufficient water, good shoes, a comfortable pack, and a warm, dry place to sleep. On a short trip, you don't even need much food.
Make a suggested gear list for the new people. Make it fairly detailed (x pounds/calories of food, x liters of water, waterproof tent (Test it!), a well fitted pack (Try it first!) specifics items of clothing). Tell them to practice walking around with the weighted pack beforehand, in whatever shoes they want to wear. If possible, go on day hikes with them carrying a weighted pack to ensure that they do this.
Newbies make mistakes, and a one night trip minimizes the consequences. Plan to cover less distance than you think you should. Five miles is plenty for day 1, or just 2-3 miles if it's steep. It'll let you get a late start and still be feeling good when you make camp. The second day can be longer because you'll end up at home in your own bed, but still keep it to under 10 miles if it's flat, or under 5 if it's steep. You're with people who aren't used to hiking with weight. It's very different than walking around carrying nothing.
This answer is based on my experience not following these guidelines. I went on a 3 day hike with two people who regularly run marathons, but had never been on more than short day hikes. They're used to suffering for the sake of fun, so it worked out, but they had a lot of trouble despite a high level of fitness. One of them had borrowed a pack the day before from someone who was 8 inches taller, their tent leaked badly, they carried about a week's worth of food and lots of unused gear, and we ran short of water (I carry a filter, but it was a dry summer. It took a while to find a stream that hadn't dried up). At least their shoes fit. But running 26 miles non-stop in under 4 hours turned out to be poor preparation for hiking 8 miles carrying 40 pounds on your back. And if a newbie hasn't tried hiking with 40 pounds, they won't realize why they should try cutting that down to 20-30 until it's too late.
As mentioned in other answers, starting with a short hike is good. A week-long monstrosity through rugged terrain, while possessing a high "cool factor," isn't ideal for getting new backpackers hooked. Rather, I'd aim for a short one-or-two night hike where bailing out midway through is still an option. When I was a kid, I remember my first overnight hike was still within a three or four hour hike to the car. That way, if something went really wrong for someone in the group, getting back to the car and civilization was still possible.
With regards to gear selection and packing, providing them with some guidelines (and "must have"s) is a great idea. In one organization I was in, the standard procedure for everyone's first overnight hike was to bring your (completely packed) backpack to the meeting before the hike, unpack to show what was in it, then repack. This probably is more reasonable for kids than for adults, but offering to look over what they've packed might be appreciated.
The last thing I'll mention is that you might need to bring slightly more stuff just in case they forget something. When I'm driving people to a trailhead, I'll put some extra water bottles/food/first aid materials in the car in case they forgot to bring enough (underestimating water needs is probably the most common error I've seen). Obviously you can't carry enough water/food/gear for two people, but having extra in the car and asking if they need some before departure can save worlds of pain.
Oversee their packing or even pack for them. Chances are if they rarely hike they have little if any backpacking gear. Be sure they do get whatever they need. I would take them on a shopping trip (to my garage) and help them pick and adjust the various equipment I would recommend they take. Make sure the packs and shoes feel comfortable.
Go well under your limit for both distance and weight. Pushing yourself is almost certain to be beyond their comfort zone. Plan extra rests and view points if possible and probably avoid steep climbs.
Carry extra first aid supplies especially foot related supplies. Minor injury or irritation is pretty common when doing something you aren't used to. It may be a good idea to take a shoes off break at some point early on to be sure they aren't trying to hide problems, people can get their pride set in unhelpful ways and may have ideas about "toughing it out" that are best avoided.
Plan entertainment of some kind for the evening. A fire, some stories, a lesson in knots or field craft, maybe a game. It doesn't have to be much, but if you do anything to set the experience apart from hanging out on a couch it will make it special.
Consider de-fussification. Bring a secret treat, comfort item or present for each person to be used incase of panic. Chocolate generally goes over well. Unexpected pillows can really change a new backpacker's out look.
A couple points about leading a trip that seem to have been missed: Tell someone where you are going and how long you expect to be out. And make sure you know what rules apply to the places you will hike, camp and park.
I've done this a few times with about 30 people in my hiking and camping group. My main preparation was in selecting a place that was as safe as possible. The lake we camped on is surrounded by a loop trail of about 11 miles. So the first day is 6 miles and the second day is 5. However, there is an easy to walk, but unmarked, one mile path to a road that leads to the trailhead. Every time I've done this, a few people need to take the shortcut out and I have a co-host to guide them. The guide then walks another mile to the cars and drives back to pick them up.
We also use the shortcut to carry in a few extras, such as supplies to set up a latrine, a good size first aid kit and a cache of extra potable water. I want this to be a moderate experience of backpacking for my friends, not a chore for them.
The campsite has access via a forest service road with a locked gate. I prepared instruction to give to emergency responders on how to drive to the site, if needed. And I let the US forest service office know we will be at the site. It is a good idea to have the direct dial number for the proper emergency services in case 911 (or similar) does not work at the location or directs you to another county's service. If you do not know that cell service is available at the campsite, determine where usable service may stop on the way in or scout out the surrounding area's service availability in advance.
Been there, done that. Everyone survived, but one had to get plucked off the cliff by a chopper.
Ditto Karen, apnorton, & dirt. Unpack together before trip, repack together. Pack 2-3 heaviest items within easy reach so you can exchange them depending on who's struggling to keep up. Be ready to carry all the heavy gear and extra water yourself.
Also be sure to stop 1 mile in, make everyone take off their shoes to check for hot spots, and apply moleskin now. Newbie campers--even runners--usually don't recognize pre-blister hot spots. Your shoes wear differently with a pack on terrain vs. running on flat.
Also grill them repeatedly on basic survival, before and on the trail: "If we get separated or lost, what are you going to do again?" Make a joke out of it beforehand. Tell them you'll just be asking it to see how they're faring on the "death march." But you need them to constantly be thinking about their response so they don't run or follow equally foolish "instincts" when they get surprised/adrenaline. Telling true good/bad stories is a great way to do this.
Beware the prideful ones. They're quickest to take off in a dead run when they think they've lost the trail, rather than stopping to reconnoiter.
I am assuming you go with adults. They are adults and you don't need to babysit them. Tell them what to take and what to not take, but gear inspection or packing for them? The %&$*? If someone is insane enough to go on a snowy 2500m high mountain in sandals (twice!), it is his problem.
1.) Make the trip interesting. This is by far the most important part of the thing. Nearly getting them killed - they will at least have stories to tell, even if they never go again. An easy 10km trip on the forest trail, sleeping there and going back will be likely boring enough they won't consider going out again.
2.) Too difficult, not enough food, not enough water? You will manage somehow. But don't go crazy. A 50 km trip in 2-3 days over few mountains (2000m height difference per day) is a nice starting experience if they are in reasonable shape, even if they aren't really used to walking. Just make sure an abort is possible at any time - "rescue" needs to be at max few km away. Plus possibly 10-20km walk of one person to get the car, or calling a cab or some other friends to get you all out of there. But if they barely manage to walk 5km on a flat surface without backpack, it is best to simply not go on an overnight trip yet. Find a nice easy 2hr walk to destination and practice on that.
3.) For a short trip, food is mostly irrelevant. 2-3 days hiking without any food won't kill them, but they will be hungry, tired and easily annoyed. Won't be a nice experience for anyone. Ask them to grab sugary snacks, to eat breakfast before you go and pack a few sandwiches and some fruit. Tell them to not take fatty and salty snacks (chips, flips etc). Water and other drinks are more important. Ask everyone to bring about 2l/day. Mostly water, maybe a bottle of a sports drink. This is also why trip should be short - 1 week requires tons of water or searching for streams.
Other stuff they need to take? A towel, spare clothes, medical plasters (preferably blister ones). Sleeping bag depends on the area and weather. In spring/summer can usually go on a trip without and not freeze. If they take it, they should have a light and small one for spring/summer. Not a winter one. Too warm, too heavy.
It is very likely they will try to take too much stuff on the first trip or forget something. Put a lot of emphasis that every kilo counts and that you will all stink together :)
You should pack all they do, bandages and other wound treating stuff (disinfection, soothing etc), extra chocolate in the morning to get them going, tent of course. Maybe flashlight, compass, map (phone can replace these 3, as long as it is charged :) ).
4.) On the trip, make sure you all stay together at all time. Never give permission to go ahead or stay behind, unless the destination is in sights.
Make the first stop early enough, say after 30 minutes. Ask them how it is going for now, and ask them to check their feet if there is anything red. Put plaster on the area. Then stop every 2-3 hours for several minutes and check their condition.
Make sure you are setting up tent early enough.
Hmmm, people with no real experience, no cardiovascular fitness, no strength to lug a pack around, no navigational skills, I would say heck no. The first time we did it we almost bought the farm, got lost with no gear, no winter protection and we were only a bit more than a mile away from town. It was not our fault, the Ranger gave us wrong directions and sent two newbs through the forest with less than an hour of sunlight left. A forest with bears, rattlers and gators. The point is, the unexpected happens to those who are not prepared.
They should not be using their first experience for training. Trial and error, that is not the way to go out there. Have they watched the necessary vids on youtube? Are they members here? Your training begins and ends at home in safety, because if you can not do it there you can not do it anywhere.
Does this group know how to stay together, how not to panic if they see a bear? Do they know how to walk around without injuring themselves? How to avoid snakes? Nights get cold in the forest, it was 73 in the day and 38 that night that day. Easy to lose the trail, easy to lose the rest and be stranded.
First timers have no idea what it is like, I suggest take em down a well known trail, walk them down it for about an hour or maybe and a half and then bring em right back to the car and home. That should be more than enough.
Just in case you decide to not follow any of my recommendations the number one thing I can say that you should make sure everyone carries is water! Most first timers will try to get by on 20 ounces of water... Let me tell you this, there is no worse hardship then being short on water. Make sure everyone carries a gallon of it. Then comes the pain of carrying it. Good luck!