Here's a book I've referred to all of the time:
The Guitar Player Repair Guide - 3rd Edition by Dan Erlewine
ISBN-10: 0879309210

It is chock full of information about how to setup, maintain, and repair acoustic and electric guitars. It even gets into complicated stuff like refretting, repairing necks, etc. You may not do much of what is in there, but if you need a serious repair in the future, you will know what is involved and what questions to ask the luthier.

This book gave me enough confidence to try setting up my guitars on my own so I can experiment and get it just the way I want.