I did two weeks on the Florida Trail in 2006. Some things I learned/found helpful were:
If you will be in an area where you might encounter mosquito's, ticks, biting flies etc. bring plenty of bug spray. They can make you absolutely miserable.
Bring some kind of pillow. I didn't, figuring I would use my pack or extra clothes, but wished I had. A good sleeping pad is also a must.
Pack a small, thin towel. You don't need a full size one, and thin will dry faster.
Invest in several pairs of good synthetic or wool socks.
Cotton clothes suck. They absorb moisture and take forever to dry.
You will eat less than you think, but pack plenty. Good staples are ramen noodles, quick cooking oatmeal, and trail mix. I would cook oatmeal and mix in some trail mix to add some flavor, and snack on the trail mix throughout the day. I also like to stuff my cheek with sunflower seeds and eat them while I hike, gives you something to do and the salt tastes great.
Wet wipes!
Gold bond powder, for your feet, crotch, armpits, everywhere.
Water proof you tent thoroughly before hand, also practice setting it up.
Bring some "100 mph tape". It is an extra strong military version of duct tape. You can use this for just about anything, patching holes in your tent, repairing tent poles, fixing shoes. While you are at the surplus store pick up some parachute cord as well, light and strong, you can also take it apart and use the small inner cords for fishing line or sewing thread.
Learn a few good knots.
Avoid packing things in rigid containers as much as possible, using sturdy flexible bags saves space and allows more flexibility in packing.
Make a good walking stick.
Bring a multitool and a larger fixed blade knife for things like chopping and digging. Don't forget a small sharpener of some kind.
Bring a bic lighter as well as waterproof matches or a fire starter.
A good hat and sunglasses are essential, as well as good boots. Break the boots in and water proof them before you go.
Underwear is unnecessary.
Strong black garbage bags have many uses, as a poncho, tarp, to keep wet things separate in your pack.
Get a good map of the area you will be hiking study it and commit to memory as much as possible.
Even if you have a gps, bring a good compass, and know how to use it with a map.
A led headlamp and small bright led flashlight. Don't forget extra batteries.
I don't know if you smoke, at the time I did, nothing like a little bit of high test after a long day on the trail to relax.
Brush up on first aid. It's a good idea to pack a sheet with first aid instructions in your first aid kit. Military surplus has nice compact kits, the wound dressings that form clots to stop heavy bleeding are good to have. Pack benadryl in your first aid kit, if someone has a bad allergic reaction it could save your life. If you have a known allergy to insect stings you should bring an epi-pen.
Make sure you are staying hydrated even if you are not thirsty.
Get used to walking before you go, take day hikes with an increasingly heavy pack leading up to your long distance hike.
Get a full body massage when you get back from your hike. My shoulder muscles were so used to having a pack on they thightened up on me when I got home. That massage was the best feeling I have ever had in my life, better than getting a blow job while hitting a hole in one with a winning lottery ticket in my pocket, seriously.
The first week is the hardest, after your body gets used to the routine you will become a machine.
