All the permethrin recommendations are great. My personal experience has been that I've successfully avoided tick bites (so far, knock on wood) since I began using the stuff.
I'd like to also endorse carrying a small mirror while out in the woods for conducting regular tick-checks on places where ticks like to hide (waistband, armpits, rear end, etc). In the event that you do get one on you, getting it off quickly can reduce the risk of contracting a disease. More than a few friends have come home from weekends camping only to find engorged ticks clinging to some very sensitive areas a few days later.
I'd like to also endorse carrying a small mirror while out in the woods for conducting regular tick-checks on places where ticks like to hide (waistband, armpits, rear end, etc). In the event that you do get one on you, getting it off quickly can reduce the risk of contracting a disease. More than a few friends have come home from weekends camping only to find engorged ticks clinging to some very sensitive areas a few days later.