Humm. Believe it or not, may be a bit too broad a question. What you do mean?
Trails and routes:
Sierra South, and Sierra North guide books. (probably one or both of these if you are planning a fist trip)
Sierra High Route, Steve Roper (maybe this is too ambitious until after you are much more experienced in the area)
Any of the JMT guides (great for everything about the area, except the other specific routes)
(all of the above have some discussion of weather, gear, etc. before the route details.)
Mountains to climb:
The High Sierra, R. J. Secor
The Secret Sierra, David Gilligan
Geology of the sierra Nevada, Mary Hill (really fantastic book, probably have to buy used)
The Sierra Nevada, (Sierra Club Guide) S. Whitney (might also be out of print)
History of the Sierra Nevada, F. Farquhar (a bit dry)
Discovery of the Yosemite, Lafayette Bunnell
Mountaineering in the Sierra Nevada, Clarence King (nice historical record of exploration of highest part of sierra)
Possibly one or more or the better JMT blog/trail journals would give you a very good idea what it is like to backpack, not to mention the omnipresent JMT gear lists on here.
The list goes on and on -there was someone on here that compiled a bibliography just about the JMT and it was pretty huge - I think over 50 books on the JMT alone.
If you are starting from absolute zero then IMHO the first thing to read is "My first summer in the Sierra", John Muir. Nothing about gear or techniques that any sane person would be able to imitate, but essential reading nonetheless.