these guys here know what they are talking about, wish I had them 25 years ago, I'd be a lot stronger player than I am today if I did thats for sure.
to answere your question,I know a pile of pros and what they do. Some play 14.1(straight pool), others practice shots they miss the most often. Some shoot drills like the guys here are talking about, or any of the 3 things I just mentioned.
I missed a ball once that cost me $100, so fo a week I shot it 100 times a day from both sides. I got to the point I didnt miss it very often-it was a kinda hard shot, I still to this day practice that shot once a week and if I like what I see I move on, if I dont i stick with it.
where the balls are randomly spread on the box is damn near irrelevant for training and practicing in the proper sence of the word. And isnt a good start to practicing to get better. What counts is how do line up, hold the cue, breath, look at the balls, which ball do you look at last, haw many warm up strokes do you take, do you stay down after the shot, or flip open your bridge hand after pulling the trigger(a bad habit I have when I'm not playing daily). When it comes down to it the shot selection of which balls when practicing is a very very small% of whats really going on.
you can take that info to the bank,
I dont think any of these top instructors are gonna argue much with what I just said, and if they do I'd love to hear it-i might just learn something and thats awalys a good thing.