I think one of the biggest things is to make sure Poker doesn't eclipse the other things in your life. The more it matters to you, the more these things will upset you. Make sure you have friends, or a lover, or something to distract you and provide fulfillment in your life. If I spend too much time playing I find that it's harder to brush it off if the session doesn't go well. I don't think I'd ever want to be a professional poker player, for that reason. (As though that's an option)