One good way to do this is to practice hitting your shots while your partner actively tries to rattle you verbally. Review my article on Attentional Control in Tennis . Lower your own unnecessary ideals. You want to impress yourself as well as others, but the problem is that you think your shots should look perfect, that you should never miss, or that you should appear really impressive. This is deep fantasyland.
Tennis is a sport in which staying in the moment and reacting effectively to adversity is rewarded.
There are no form points awarded and you only need one more ball over the net than your opponent to win the point. Work on your technique and style in practice, but once the game begins keep your mind on staying in the game and exploiting weaknesses. Work as hard as possible to keep your energy level down in front of a crowd. Remember that the tendency is to become over-energized. Fight this urge by breathing deeply, slowing down your actions, and remaining focused on the task at hand.