[HamBungler]

Playing with other players, especially if they are much better than you and are good teachers. Having someone who is better than you gives you a good idea on how good you want to get, then just pick their brain of everything they know, jam with them, learn some riffs they've made up. When I was still in Vortex of Corruption, I probably got better most quickly when playing with our lead guitar player, he forced me to better my technique, pick faster and cleaner, and do leads. This really helped me out and I'm a better player because of it.