You will be amazed how much better you will play when you concentrate on getting away from the ball. Remember when you were a kid and you played "dodge-ball" at recess... what did you really want to do? -- get away from the ball! Same is true in tennis.
Most players wait for the ball to almost be on top of them and then they contort themselves to hit it. Watch the pros. They get so far away from the ball that they come back at it to hit it. This way you have so many more choices where to hit the ball. You want to hit the ball to your side. Think about where the batter stands to hit a pitch in baseball. Your ultimate goal is to get away from the ball when it is on your opponents' side of the net. Then, when it is on your side you can go more to it, instead of falling away from it. Many times a player will make unbelievable shots while running for a ball, but will make tons of errors on the balls that come at them. This is a good reason to stay away from the ball. This idea can also be carried over to overheads. When it comes right down to it you want to contact the ball as far away from you as you can reach. This concept is far more important than power.
When hitting ground strokes, approach shots and volleys, think about the number "7" and the letter "L". As soon as you can, get off the ball like the short staff of the number "7" or the letter "L".
Of course, you should take the path of the long staff in parallel with the center service line.
Get away from the Ball and Good luck on the courts!