Have you ever wondered how the pros can direct the ball seemingly effortlessly?
 
They can send it down the line, then cross-court at will. It's not as easy as it looks.
 
Try this. Let's take the forehand groundstroke for example. Instead of saying "down the line," we will say "right." Instead of saying "cross-court," we will say left. When you want to hit your forehand to the left, try to position yourself closer to the approaching ball. You will see that by getting nearer the ball, it will force your shot to the go "left." When you want to hit your forehand to the right, try to position yourself farther away from the ball. You will see that by positioning yourself farther away from the ball, it will force your shot to go "right."
 
Soon, you will see one of the most common mistakes in tennis. That is, in our example with the forehand, lining up too close to the forehand and trying to hit the ball "right" or lining up too far away from the ball and trying to hit it "left." Sounds simple! Many times you will know where you want to hit the ball, but you are not matching your position to the ball before you strike it. Always, hit your shot according to how "near" or "far" you are from it, instead of just where you "want" to hit it. Better to hit a shot that you know where it's going and that will go in, instead of fighting centrifugal force and making an error. This works on backhands and volleys also.
 
Good luck on the courts!