It is easy to over analyze what is going on in a tennis match, especially if you are the one competing.
Try to start the point with a very simple idea: If you are the server, focus on getting the first serve in. I would recommend serving to the middle of the box initially to help increase your first serve percentage. Once the opponent makes the return, hit the next ball to the opposite side of the court from where the return of serve was hit.
Continue the point with two or three crosscourt shots and then look for an opening to win the point. Many points will end before you have to hit that winning shot. If you are the returner, focus on making the return to the opposite side from where the opponent served from. Continue with two or three crosscourts and look for an opening to win the point.
This strategy is simple but if executed well, you will be in a much better position to win the match since your early point unforced errors will likely be minimized. Keep your ideas simple!