Eflers has a speed control dirll. Example is on the Carombooks web site. Not sure if the speed "drill up and down the long rail" is in the book but that's a good one too. Hit the ball so it stops in defined areas. Start with 2 diamond quadrants then graduate to 1 diamond.
Practice the most basic shots. Mark the positions to be sure you're shooting the same shot every time. Then go to the hybrids of these basics.
Practice tip placement and study the effect. Shoot across the short rail and determine where your tip must be to come back one diamond from the starting point then 2 diamonds and three. Now that you're calibrated go back to basic shots and study the effects of your tip placement per a given hit. Start with half ball hit and all tip placements. Pay attention.
Now divide the long rail into thirds and and go to basics and tip placements within each third of the table. Don't forget the short rail.
Do the up and down, back to the tip drill. Helps with many aspects of stroke, aim and of course knowing center ball.
Drill on feathering the ball at all distances.
After that practice the shots you consistantly miss. Again mark the table.
Last but not least study some of the major systems and master them. Divide the table, tip placement, hit variances. Whether you want to use systems or not there nice to know. Its a double check on instinct.
This ought to keep you busy for about 40 or 50 years.