When you take a lesson, you often train by repeating the same shot over and over (like a ball machine). However, in a competitive match each ball comes different, fast/slow, topspin/underspin, deep/short, high/low, etc. The variables are unlimited.
 
What is a good way to handle all of this? Adjust constantly! Let your shot selection be determined by the depth of the shot, pace, height, spin and your location versus your opponent's location. Allow your opponent's position versus your position to be paramount. For example, in a match do not think about where you are going to hit the ball in advance. Wait and let these other variables enter into the equation.
 
For example: if you are being attacked, try to defend. Ask yourself when being attacked: Is my opponent attacking and coming in or are they attacking and staying back. This determines whether you are defending, neutralizing the shot or going for an offensive passing shot.
 
Tennis is a game of making constant adjustments. You need to make your final shot decision determined by many variables. Allow these factors to help you choose how you are going to hit the ball. Quit going for your "dream shot" all the time. It just won't work. Play against your opponent, not the tennis courts.
 
Good luck on the courts!