- Inspect your camping spot for ticks first.
- Nymphs are really, really tiny.
- A touch-check is not enough, get a visual check if you can.
- Get the ticks off your clothes before you enter the tent.
- Know when you are the most vulnerable.
- A no-see-hum mesh will help, but may not be enough.
- A blood test may reduce the risk of unnoticed Lyme disease.
It is more risky than doing day hikes, but here is what I've learnt the hard way:
First, on camping spots: If possible, avoid any kind of vegetation on the ground (for example: dense pine forests are ideal). Otherwise, roll up a sleeve and carefully go with your hand through the grass that would receive your groundsheet, plus a 1-2m safety perimeter. Check that arm often: if you picked up any tick, nymph or larva in the process, go somewhere else. It doesn't have to be far away: I've found a clean spot just four meters away from an infested place. You may speed up the process by using some kind of clear cloth instead of your hand, but I'm not sure it is as effective.
Then, be aware that until mid-August you'll also meet nymphs (1.5 mm unfed), not just adults (3mm unfed and bulkier). They're just as dangerous. In fact, some researchers believe that nymphs are responsible for a large majority of cases.
Nymphal ticks cause most cases of Lyme disease. Because nymphs are as small as poppy seeds and their bite is painless, people often don’t realize they have been bitten. Adult ticks can also infect humans, but are easier to spot and remove.
You probably won't feel any bump when touch-checking yourself if it hasn't fed on your blood yet. I suppose you can feel an engorged nymph, but I didn't test that myself. Also, while you may feel the itch of an adult deer tick crawling on your skin, the nymph goes undetected between your hair. So it is better if you and your hiking companions can check each other visually, instead of solely relying on your own touch sense. Otherwise, bring a small mirror as suggested by @Kyle.
Also, think of how you'll go from fully clothed outside of your tent to checked inside your sleeping bag with all ticks out. I have some sort of groundsheet extension where I undress and check myself outside of the tent without being in contact with the ground. I also check my clothes inside out: I once had several nymphs wandering between my clothing layers, probably picked up while pitching the tent.
Speaking of which, I found that I was much more vulnerable while camping than just hiking. Pitching, digging the latrine, tending my feet and knees are all activities where I am close to the ground and where ticks may climb onto unprotected body parts (wrists, legs after undressing etc.). Conversely, when hiking I can wear light gaiters to protect my ankles and I can check my pant legs often if I have to go through high grass areas. YMMV, just be aware of when you are taking the most risks and learn to develop a healthy paranoia of all moving or unusual black spots in your close proximity.
On tents and nets: I wouldn't consider sleeping in tick territory without one. However, I've seen (harmless) larvae go right through my no-see-hum mesh, so I'm not positively sure that it will keep all nymphs out. It will block the adult ticks, though.
I did not try Permethrin, because I'm not too thrilled about handling a likely carcinogen without a mean to shower it off at the end of the day.
Lastly, once back home you may do a blood test for Lyme disease. Just be aware that these tests are not 100% accurate and may produce false negatives.
Conclusion: there is no such thing as perfect safety, but I now feel "safe enough" when applying the above tips.