How do you overcome nervousness or the jitters before a big game or match?

I remember my first tournament as a little girl. I think I was 8 or 9 years old. I remember drawing the number 1 or 2 seed the first round. I was so nervous and knew I was going to lose. My Dad took the approach that this girl whoever she was, was no better than me and that I was being silly for doubting myself. So I sucked it up and went out there about to throw up but ended up beating the little girl in straight sets. I have no idea what I did or didn’t do. I just went out and hit the ball, which is exactly what my Dad wanted me to do. The minute you think about winning and losing you are taking your mind off the game. And for sure the minute you think you are going to lose that is exactly what will happen. My tools to children now would be to give them a sense of confidence, a cocksureness, all athletes have to have that, but not a cocky-ness, there is a difference! And to try to be still inside, to know that you have prepared as best to your ability for the match, and to trust yourself. Go out there, be smart, play hard, and give it 100%.