Top 3 drills:
Rotation, Rotation, Rotation....
If your fundamentals are close to sound, 15-ball rotation will dial in your control and touch and make you comfortable with non-standard positional shots, as well as require you to maintain focus and recover from any mistakes through a long rack (play every ball, not just to 61 points, you want to train yourself to finish racks strong and not get complacent on the last two balls)
I personally don't see repetition drills as particularly appropriate unless you're dialing in something with your fundamentals. In real play you're going to be playing a variety of shots with different methods of control, not repeating the same shots, so you need to mentally prepare to have to hit any shot at any time.
Darren Appleton also has some decent drills where you pick off a carefully ordered pattern going to a rail and back each time that are important for speed and angle control off rails but once you know *how* to go through the setup to get comfortable with CB control methods you're weak on, I think it's better to just play rotation and mix it up. If you can get through a 15-ball rack 1 out of 4 times, you're doing pretty good.
The BU exam is 'okay', but to be honest it's geared too much to 9-ball and you won't really test yourself on some of the more difficult patterns you can encounter in 10-ball, 15-ball rotation, 8-ball, or even straight pool. The BU exam does't test your ability to make more aggressive plays, bend the CB off cut shots, reverse your angle with draw off a rail, take 4 or 5 rail positions, drag the CB straight down a full table length off a cut shot, or intentionally hop the CB after contact with force follow over an obstacle.... these shots actually can be incredible useful for recovery shots or dealing with problems while you still have insurance balls on the table when you would otherwise be forced to settle for a long pot and try to get back in line over multiple less than ideal positions and hope to solve your problems at the end of the run. 15-ball rotation is always a challenge and will make you more creative and less timid with truly difficult situations. The BU exam *is* good at test your angle judgment on rail shots and general pace control on certain types of safeties where you have a cluster to hide behind, but you can only practice safety play so much on your own, 90% of playing a good safety is not chickening out when a live opponent is waiting to come to the table to punish you for a mistake.
