- If there is another person person onboard, have them do nothing but watch the person in the water. They should point a finger at person in the water and never take their eyes off.
- Toss out life buoys, life slings, floating cushions, etc.
- If you have it, hit a man overboard button on your GPS. If not, make a waypoint.
- Stop the boat, lower the sails.
- Motor back to the person in the water. If possible, drag a rope with a float (life jacket, life sling, etc.) on the end to the person can grab it. If that's not possible, throw the rope or get close and try to get the person to swim to the boat.
- If at all possible, do NOT get into the water. Only if the person is incapacitated or incapable of holding into a rope should you consider it.
Think about doing this at night. If the boat is beyond swimming distance of shore, be sure everybody on the boat has a life jacket (and hopefully a harness) with a strobe whenever they are on deck at night.
It's pretty difficult to climb onto some boats from the water. You should find out the best way to do this in your boat.
Losing someone overboard is probably the most dangerous thing in offshore sailing, and it is almost completely preventable.