Coming late to the question, I haven't read all the responses. My favorite stroke drill was to lay a long neck beer bottle on its side and stroke through the hole to touch the bottom without touching the bottle with the sides of the shaft as it passed in and out of the mouth.
I did always try to balance my practice with competition. The competition showed me where I was but didn't allow a chance to improve through experiments or repetitive exercises. I also tried to balance my play between matches that were easy and playing better players. The first financed the play with the second.