Never show worried facial expressions or noises when things don’t go your way or else this will make the other player’s confidence go up making him play very well. When you are confident, no matter what type of player, you will play very well. So this will make you lose the match. Keep your racket up, and be aggressive toward your opponent.
Be consistent. Even if your style is an aggressor, don’t go for a knockout winner on every shot. You can easily donate the match to your opponent before you know it. Use topspin to hit deep and set up points, always directing balls to your opponent’s weakness if possible. Chances are they will miss if you get enough balls back so don’t always try to be like Andy Roddick.