Forehand Topspin Follow Through

http://www.PingSkills.com - Ask the Coach Hi everybody, I would like to have some advice about the forehand topspin. I think my preparation to the shot is quite good (right foot behind to form a side angle of 45 degree, bat behind the right knee) but i still have some trouble with the follow-up after hitting the ball. I know I have to swing the arm till , as you say, the imaginary line between head and shoulder. If I am able to do it during shadow playing when I actually hit the ball (as friends told me) I instinctively stop the swinging too early with the result that the ball has little spin. Moreover it seems I tend to lean backward with back when I'm taking the shot. I've been trying for weeks to correct such mistakes but I can't find the way out. Are there any exercises that can help me ? Thank you very much Vito