There's nothing more redundant than shooting balls endlessly. I'll go to a table, dump the balls off the tray, and shoot them all, then throw all the balls back on the table and do it again. After two times, it gets boring for me, Great for loosening up, but you'll fall into a pattern - a pattern you won't see had you broken a rack. That said, I always work outside to in, pocketing all balls along the rails blocking other balls first, then hit the rest of the balls along the rails, then any ball in the middle blocking another ball or balls in, etc. Some people do it the other way around, but I try to avoid a half-pocket shot whenever I can.
To note, I do NOT do the three-ball-drill with ball in hand. I throw the cue ball randomly on the table as well. That's a little more realistic to what you'd see when you get back on the table in a game of 9-ball. Whether you're snookered, have a long bank, thin cut all the way down the long rail, off-angle kick, etc., and you make the shot AND get some kind of shape on the next ball, that's when you can turn the table around in a real game.
I'm not a great player, but I feel I'm a good shot and definitely better then my friends I play with. Even then, they have the ability to cut a ball, make a rail shot, even bank a few. Sometimes better than me. The difference is I can play position pretty well, so I rarely have an "impossible" shot for a next shot.
