Getting together with a good instructor is always a good idea. He will be able to work with you on your weaknesses. An area that most of us need is position play. With all or most of the balls on the table it is often difficult to move the cue ball around for position on the next shot.
I worked with Joe Tucker for a while. He empasized learning how to move the cue ball using different routes for the same end position.
From my experiences playing and watching many apa matches, I feel the number one thing that is overlooked is how to play safeties. I think most lower level league players and some higher rated ones will not even look at the possibility of a safety. Yet, if you prevent someone from making a shot you get back to the table and maybe ball in hand.
Of course learning to kick out of safety goes hand in hand with locking up your opponent.
