Step 1 - Practice these two simple exercises to get the right topspin feel.
[youtube https://www.youtube.com/watch?v=iRaONZgUg-k&w=420&h=315]
Step 2 - Follow the progression as shown in this video to develop the correct technique
[youtube https://www.youtube.com/watch?v=nNvD7-KbcEA&w=420&h=315]
Step 3 - Learn to add power by bending your legs more and throwing the ball further into the court. A quick tennis serve is also the result of a softer arm.
[youtube https://www.youtube.com/watch?v=YZxK8YBJqNQ&w=420&h=315]