get phil cappelle's book: Play Your Best Straight Pool or Play Your Best 9-Ball.
Both cover position play.
But those are just for the times when you're NOT playing.
When you are, this is what I do (and have been doing for 6 months, since I started wanting to become much better):
set the table up with two balls plus the cue ball, the objects anywhere you want. give yourself ball in hand. shoot whichever ball you want from wherever you choose. at first, just shoot it naturally, however you might want to, as a shotmaker. shoot it a few times from the same position. each time, take note of how the cue ball travels on that shot, relative to your angle, english, follow, etc, that you naturally played with. pay attention to where the cue ball ends up in relation to the object ball, but don't worry about it. just keep the relationship in your head.
next, start trying to tweak the shot a little bit so you can try to HIT the second ball. mess around with different spins and stuff. you'll end up finding ways of HITTING the second ball.
next, place a third object ball on the table from a place where you'd like the cue to be for a good shot on the second ball. shooting the same shots as before, try to experiment until you can drop the first ball and gently hit the third ball so the cue ball ends up right where the third ball was.
once you've done this for a couple of hours, you'll have a basic feel for each type of hit on that one shot, which can carry over to all other shots, in some way. do this drill once per week.
some people might tell you to first read up on the theory behind everything, then to try this type of drill, but i found that doing it in that order caused me to learn at the table by THINKING instead of learning by FEELING. instead of focusing on FIRST dropping the ball in question and THEN on position, I would just overthink the position play and often miss the primary shot...
also, i would end up frustrated that the theories weren't working for me. instead, by switching to the 'exploratory' method, i never had anything to get frustrated about. instead, i just tried things and watched what happened, learning as i went along.
eventually, you'll start stringing more and more balls together (starting out with 3, 4, 5, etc)
as you will read, good position requires you to think a few balls ahead, but remember - you're always just trying to get the cue ball to the NEXT position.
you have to know what that position should be, but aside from that, act like each shot is your next-to-last shot in a $10,000 game and you'll learn a lot about how YOU shoot, what YOUR habits are, and not focus so much on what the books say...
