Many players preparing themselves for a match or tournament will have the tendency to overtrain. They tend to hit too many balls for too long, hitting too hard and with no purpose. By the time the match comes, they are arm weary, too tired and "brain dead."
Try not to grade your improvement by quantity time. Instead, practice smarter and enjoy quality time. When practicing, concentrate on shot selection, changing spins and speed, depth, control and consistency. Thus, when you get in a match situation you will already have a general idea of what you can expect from yourself. In the match, remember your strengths. In practice, work on your weaknesses. Maximize your strengths and minimize your weaknesses in tournament play. By doing this you can show up for your match with a fresh arm, refreshed body and a fresh outlook.
Good luck on the court!