I did a lot of backpacking on Colorado in the 70's and early 80's. The previous posts have some great ideas! Here are my additions to thier suggestions:
Work on your flexability. Stretch before going out.
Learn outdoor safety, the military survival guides are useful.
Carry at least 1 qt of water. Have a way of making more.
Carry a staff. Use it for stability when crossing water, checking undergrowth for snakes ect, and as a weapon if needed.
Buy quality lightweight equipment once instead of cheap heavy crap twice.
Learn navigation. Carry maps, GPS, compass etc. Incorporate geocaching for added adventure:
www.geocaching.com
Flyfishing remote areas is awesome.
Learn rock climbing by going sideways instead of up/down. Find an outcropping of rocks and go along it, never over 2-3 feet from the ground. You will strengthen your entire body with low risk of injury. In Alaska they practice iceclimbing and rock climbing right off the side of the road. No dues!
I hope you enjoy yourself!