The best habit someone can have is to never forget that it is just a game. Dont ever let your frustration and competitiveness cause you to not have fun. None of us are professionals and we all do this for enjoyment, not to leave angry just because we lost a game or match.
IN THE END IT IS JUST FOR FUN !
As for a playing habit - Always keep your knees bent and stay low. That second it takes to go from standing straight up to getting low is the one that lets the ball pass you by!