I read/have read books, pool magazines, watched video (YouTube-type stuff), watched instructional DVD's, went to pool school (randyg), been to professional tournaments, watch live-streaming, stay involved on league night/tournaments when two high-level players are going head-to-head, things of that nature.
OTOH, probably for all that I do to help my game away from the pool table, I counteract with things that are unproductive to my game. I do not exercise (I keep saying I am going to start walking, but never seem to get it done), I eat horribly (my favorite foods in life are not exactly what one would classify as "health foods" :embarrassed2

, and I have a varying sleep routine where I might get 5 hours one night and 8 or more on another. Some days I take an afternoon nap, sometimes not.
Besides my physical problems (bad shoulders, eyesight, etc.) coupled with a seemingly unfixable wobbly stroke, I figure I've about hit a skill plateau of which will see little-to-no improvement for the rest of my poolplaying days. I'm okay with this. I just play for the fun of it. I'm not about to give up the delicious foods that give me much enjoyment just to get 1/2 ball better. That is NOT a good trade-off IMO.
Maniac (something's gonna kill ya, might as well be good food!!!)