In a match, many times you will be thinking about winning or losing. Usually, this does not help! It might be the worst thing you can do!
With my students I encourage them to just think about winning the next point. Then try to win a series of points or "runs." Usually, the player that accumulates the most "series of points" or "runs" will win the match.
This method allows you to deal more with the present, not the past and future.
It is much better to remember that you have won the last 6 points then to worry about winning or losing the match. This can give you immediate positive feedback and motivate you greatly. Thinking about all your mistakes or lost points will not help at all! Stay in the "positive zone."
Good luck on the courts!