I found after you can run maybe 3 racks consistently, the best way to improve is to watch how great players run their patterns. If your missing balls to end a run.....you need to work on technique. On the other hand if you are running out of shots, getting stuck not opening the balls up, or not leaving/making break balls etc....you need to learn more about the game to lengthen runs. IMHO and the only way to do that is to learn from a better player/instructor than yourself.
Took me for ever to learn that you can play good 9ball learning and practicing yourself because the game is spelled out for you. Not the case playing 14.1 or 1 pocket....you must learn from accomplished players....unless you have some magical voodoo savant thing going on.;D
Gerry