I wish someone had given me a simple idea about how I should be playing points earlier in my tennis career. I think I basically hit the ball and waited to see what would happen. This sounds crazy to me now, but I think a lot of players still play like this. Here is my advice on how to play a point:
Start by focusing on the serve or return of serve and get the ball in play. Next, hit a couple of crosscourt groundstrokes to get your opponent moving. Follow this up with some movement forward, trying to get the ball back to your opponent's side of the court a little sooner than they expect. If the point is still alive, hit the ball to the opening with a little more speed, depth or angle, and try to win the point.
There are many more things you can add to this idea depending on your preferred style of play. Keep in mind that a great majority of the points will be over before each player hits two successful shots, so keep your ideas at the beginning of the point simple. Remind yourself of the basics, including early preparation with your shoulder turn, watching the ball all the way through contact, and covering the open court while expecting the ball to continue to come back. Most of your thinking should be done just after, and just prior to, playing the point. During the point, focus on the basics as stated above and try to make them habit so that there is little thinking involved.
Play all the points the best that you can and get ready for the next one.