Depends on the game. I NEVER train for anything... but if a game is fun, i play excessivly and become very good.
I am a good natural, but lack fast reflexes or encyclopedic knowledge in most games. My big advantages is a great sense of tactic, timing and experience. (I know when where who will be and what he is doing... but to kill them is another thing *g*)
I get completely crushed by Pros (harrharr), but in public games or in balanced matchmaking i am normaly a hurricane of asskicking.