Practice guitar, preferably 2+ hours a day, but I'll take whatever time I can get.
I also write my own music, though I've been a bit lazy in that regard lately. I come up with some kick ass riffs, but don't bother writing them down, and after a few weeks of playing them over and over again, I can't remember if they're mine or if I heard them in some song somewhere.
It really sucks when you can't definitively say, "Oh yeah, that's mine."