Question: How would I hit a topspin serve?
Answer: To hit a topspin serve, toss the ball so that if you didn't hit it, it would graze the back of your head. Swing forward and sharply upward, brushing your strings straight up the back of ball, in a line from 6:00 to 12:00 if the ball were a clock face. Use a grip between Continental and Eastern backhand.
Most of the full article here on the twist serve can be applied to the topspin serve.
