Not an instructor, but I'll weigh in. I like to break down positional play into 4 simple steps, and it's something I refer to as POMA.
1. Plan
2. Observe
3. Memorize
4. Adjust
You should start by planning the path of the CB on every single shot. Even when there is only one ball left on the table. Obvious exception would be stop shots. Other than that, however, start by picking a specific spot you want the CB to end on. Going to a rail (or more)? Pick specific spots on the rail you want (or think) the CB needs to contact. If you're just starting out, you're going to be wrong...a lot. But you'll find with time, you'll start becoming more and more accurate.
The next step is to observe exactly what happened. Did the CB go where you thought it would?
Thirdly, you must memorize the results of the shot. Good or bad, add it to your memory bank.
Finally, and this is more geared towards practice sessions where you can set the shot up again, adjust. If you were wrong, then make adjustments until you get it right.