I suggest some general purpose reading first, on this site and/or others.

In particular suggest one (or more) of these three:

http://www.verber.com/mark/outdoors/backpack/get-started.html
http://tinyurl.com/aulxwpl
http://www.pmags.com/backpacking-a-beginners-primer http://www.pmags.com/backpacking-a-beginners-primer

I like those in particular because they build in some discussion of keeping pack weight down from the very beginning.

There are of course also books out there, and your local library system might well carry one or more of these. I’ve not been through all of these in depth but from modest review recently, I’d suggest one of these:

- Allen and Mike's Really Cool Backpackin' Book, by Allen O’Bannon & Mike Clelland

- The Backpacker's Handbook, 4th Edition, by Chris Townsend

- The Backpacker's Field Manual, by Rick Curtis