Meditation, stay calm, relax, good sleep, be rested, and remember that the competition is against yourself, doesn't matter who you play against, that person won't change the path of the balls when you hit them. This are things I think about while a pre-match/tourney. While playing, just concetrate in the strategy of the game, when to go for the run, when to play defense, this also have to do with analyzing your opponent style, is that person aggressive or defensive? Depending on this I adjust my approach to the game.
Here is also and article I liked about a similar question someone asked to Tony Robles which answer in my opinion is good:
Dear Tony: I get really nervous before matches. How do I stop that? — L. Azariant; Boise, Idaho
Stop fighting it. You are so focused on being nervous that you are not giving yourself a chance to let go. For example, I think I’m playing the best pool of my life right now. I’m playing with so much confidence. I can go a week without hitting a ball and I come back at the same speed. I finally got to the point where I can honestly say that I used to focus on feeling comfortable too much. When I didn’t feel comfortable, I would end up playing even worse because I kept waiting for it to happen, instead of just letting go and enjoying the game. When you are worried about feeling comfortable or not feeling nervous, it’s not going to happen, because that is what keeps you on edge. You aren’t focusing on the task in front of you.
My goal, when I play is to not think about what happened in the past or in the future. But if you are thinking that you know the future, and you have a mental picture of you missing a ball, you’re actually programming your brain to do. You end up hitting the ball exactly how you pictured it. I just focus on the spot on the object ball, and trust that it’s going to go in. I rehearse the shot before I shoot. So as soon as the shot comes up, I already know where I want to hit the cue ball, at what speed and where I want it to go. Once I make that decision, I throw everything else out the window. My only job is to make sure that I keep my eye on the ball and stay down as I strike the cue ball and the cue ball strikes the object ball. That’s all I’m focused on. If you try to make the result happen and think too much, your subconscious mind will take over and will try to steer the cue ball to the left or right.
There was a point in time when I was playing that I felt invincible. But that is how you always feel when you are in the zone. It doesn't matter who you are playing. It is just you and yourself. That is how I have always looked at it. It is really just a battle between you and yourself.
Hope this helps some of you.
