I am still in the planning stages for my hike, but I just realized I am doing something in school right now that would be smart for anyone planning a thru hike or just wanting to get lost in the woods for a weekend. Take a first aid course. I am currently taking a Red Cross first aid course as my local Junior College, and I realized these are all skills that you can use on the trail. So check your local area and see if there is a Junior College or some other place offering a first aid course.
Also, while on the hammock Fourms I saw this:
http://goo.gl/c9dGuU
A very helpful guide to knots. Trust me, out in the woods you need to know your knots.