Mikey:
I'm an Open-level player (not yet a pro), so I'm not sure if by "great" you mean the pro-level. But the main thing that got me there was something that GreyGhost touched on -- proper setup and alignment to the shot. For me, that was the snooker style.
For many years prior to that point, I had probably a classic Lance Perkins pool stance (and I mention Lance Perkins' name, because I studied this style specifically). For me, I couldn't get my head/eyes into proper alignment on the shot where the shot "was comfortable from the get-go." Some shots I felt good. Yet other versions of that same shot, same angle, same distance from the pocket, made me uncomfortable. I couldn't figure this out. I would practice that "version" of the shot that made me uncomfortable, on the exact same side / position on the table, only to discover that for some reason, "now" I felt comfortable with it. What the ...?
Then, I discovered Richard Kranicki's great work,
Answers to a Pool Player's Prayers. I discovered that my problem was inconsistent head/eye alignment to the shot. The pool stance wasn't working for me, because although it's more comfortable than the snooker stance, it was "loosey-goosey on top." There was no consistent placement, other than "place your head over the cue."
After digesting this book and experimenting with my stance, I made a small jump that lasted for quite a while. But then I plateaued again.
After watching a certain snooker pro practicing on the big 12'x6' table, I was enthralled with this guy's accuracy, hitting the back of those small pockets at any angle, any speed, any distance. Previously, when I was using the Lance Perkins pool style, I thought the snooker stance "looked pansy" or made the shooter look like a fairy -- derriere sticking/jutting out like that. But that day, watching the snooker pro in action, my mind was forever changed.
I gobbled up whatever snooker fundamentals information I could find (which in the dawn of the Internet -- early 1990s, wasn't easy). I couldn't get my feet place properly, and when I did, the back of my calves ached like a son-of-a-gun. Then one day, it just clicked. I wrote a post about that experience
here. From that time on, I was easily ANOTHER LEVEL of player. For the first time in a long time, every shot looked RIGHT. Although I could always see the ghostball, I couldn't correctly deliver the cue to that place every time. Sometimes, I'd be down on the shot, "see" the ghostball and know exactly where to aim at it, only to deliver the cue and watch as I missed that spot by a good margin (and of course, exude a stream of expletives along with "how in the world could I miss the ghostball by that much??)" Now I could consistently see the line correctly and deliver the cue down it!
I wish I had more time these days to play. I'm hoping the pipeline for my information security company levels-off, and I can enjoy some regularly-scheduled personal time more often. You can bet I'll be hitting more tourneys more often. Can't make it to DCC yet, but hopefully this is the last year that will be the case. I will be at SBE, though. Color me there, for sure!
Hope this helps,
-Sean