Guess I'm old school.
The best drill for me is practicing 14.1.
14.1 is the toughest game in pool.
The constant focus it takes to remain at the table is the toughest thing in pool.
[...]
14.1 helps you work on your focus.
I'll remember this philly. Seems like good advice. I've never even tried 14.1. I agree about focus. I notice the shots I miss, and often it's because of laziness, or because the shot is easy and I don't respect it, or I'm too lazy to get the bridge out. I'm trying to learn how to give every shot the respect I naturally give to the hardest shots.
Recently I've started playing with a neighbor who is a much better pool player than I am and he's a 9-ball player. So I've just lately started to play 9-ball for the first time, which always just seemed intimidating to me. He has loads of experience and he's taught me a number of "moves" I guess you'd say.
I'm doing better than I thought I would. To the surprise of both of us I end up beating him more often than not. But that's only because he doesn't practice and I do (he only plays a couple of times a week and some weeks not at all), and I am, let's say, more tricky. He's one of those guys who either hits hard or harder. He breaks so hard it's left a bunch of marks on my table. He'll hit hard for no reason other than that he likes to, and a pocket will reject a ball that absolutely could have gone if it was hit more softly. And, he overruns position sometimes because he smacks it too hard. Plus he gets discouraged when he misses, so I can be sort of sly and win by laying safes that he just thinks are misses, and then when he misses a few he starts to lose his confidence. (I hope he doesn't read this or he'll be on to me lol.)
Seems like I can let him pocket most of the balls sometimes and even break out the clusters for me; then I slide in like a thief and win. He always complains bitterly that "I gave it to you" but hey, whoever sinks the 9-ball, right? We "don't keep track" when we play, except I do, and a few weeks ago I beat him 12-4 including 5 in a row. But he beats me too. He's a much better player than me so I'm learning a lot just by watching him. The one thing I can't get from watching pro matches on YouTube is where they hit the cue ball (except for those few matches where Earl did commentary). But with him I can ask him what kind of spin he used. He hits every ball with spin and I've actually learned to hit a few types of shot with spin, like long cuts with outside (which are actually
easier with spin, surprised me). When I see him do something I don't even understand he will take the time to explain it to me after the rack, which is great. Some of the shots he plays I can't even do because I lack his cue power. Some of his shots are just absolutely friggin' magnificent. Every time we play he will hit at least a few shots that amaze me.
Anyway if I can play 9-ball, which I always imagined would be too hard for me, maybe I could learn how to play 14.1 too. I'm going to keep it in mind. I know I can pocket 14 balls in a row sometimes, but I have no confidence that I could set up to break out the second rack. But then, if I don't work on it I'll never learn.
[UPDATE 2 hrs. later: Well I tried 14.1 for an hour and so far I haven't even gotten to the 15th ball! I did however do quite a bit of swearing, if that counts.

So maybe I'm worrying about the second break for nothing. It
is interesting though. I kinda like it, despite my lack of success. You have to plan.]