Tennis is an incredible sport. As you are learning the game, you can work on so many different areas to improve on.
Most of us initially focus on the actual hitting of the ball-strokes, footwork, placement, etc. As you improve, it becomes pretty obvious that winning a tennis match is not always directly related to how well you hit the ball. Sometimes it is selecting the right shot at the right time.
Other times it is the effect that your strategy has on your opponent over the course of the match. Even as you get older and cannot run as fast or hit the ball as hard, you can improve by being a student of your own game and using what has worked well for you in the past. Arthur Ashe came up with one of my favorite quotes for approaching both tennis and life:
"Start where you are, use what you have, do what you can."
Take a few minutes and try to grasp exactly what this means. It will give you a great chance of continuing to get better at tennis, as well as providing you an awesome model to deal with all of the things that our thrown at us in our day to day lives.