I'd recommend Cappelle's PYB8B as well. Great book.
Also good are George Fels book, I think it is something like A Smarter Way to Learn Pool.
I flipped through Larry Schwartz's book and it looked good, but I didn't really read it.
In a nutshell, you have to learn really only a few basic principles that will help across the board:
1) Learn to view your balls as tools, with a specific function. This ball lets me get shape on that tough to reach ball...this ball lets me break out that problem...this ball blocks his runout while I deal with this issue over here...etc. EVERY ball has a function. Determine that before you start blindly firing off balls.
2) Consider 8 ball to be a race to the runout. Each turn you take has a cost, which is that now the other guy gets a turn to do something. To be a winning 8 ball player, you need to maximize the value of each move you make, each turn. If you're playing safe, its better if you can play safe and also tie up the other guys ball. Stuff like that. Simply hiding the cue ball from the other guy is a pretty weak move in 8 ball. It *might* get you ball in hand, but it might not. It might just result in a worse situation than the one you're in. So consider that you have a limited number of turns to stack the odds in your favor the most you can. You are trying to get to the wide open table before the other guy.
3) Think of 8 ball games as having 2 phases. The "move" phase, and the runnout phase. In phase 1, you are trying to prepare the table for a runout that gives you a super high chance of success. If you have problem balls, you're probably not ready to run out unless you are a super strong player with amazing cueball control. If your opponent beats you to the runout, you're supposed to lose. Once the table is open for you, now you go to phase 2...runout! Sometimes you screw up the runout and have to go back to phase 1.
4) Don't forget you can use the other guys balls to play safe. When the cueball is frozen to another ball, or gives a look only at an unmakable ball, that can be super effective in 8 ball.
Keep these ideas in mind and you can play some strong 8 ball.
KMRUNOUT
PS. STUDY this rack between Bustamante and Reyes. Listen to what Billy Incardona says. I've learned more about 8 ball from this 1 rack of pool than anything else!
https://www.youtube.com/watch?v=hsCLcuLXlEM
https://www.youtube.com/watch?v=1GqrF3xS2qA