I'm brand spanking new to geocaching, but have been a hiker/backpacker for years and used to work in the outdoors all the time. I second (okay, third and fourth and fifth) everything that Briansnat said.
I typically will spray a baseball hat with deet and usually carry a bandana or two with me in my pack - which in lieu of a hat - i'll spray the cloth with deet before putting it around my neck or over my hair.
for my clothes i recommend permethrin - it's strong stuff and i've found dessicated ticks on my socks afterwards. whichever brand you choose - please read the labels very carefully - the brand I've used had to be sprayed your clothes and must dry for a few hours before putting your clothes on.
(unfortunately b/c i was caching in what i consider an extension of my backyard the past two days i got complacent and wasn't as careful as i should have been - and we came back with adult and nymph ticks on us - black legged and dog ticks. i'm still a bit wary each time i feel an itch.)
