There are two types of spin to add to your second serve. The first is slice (learn more here); the second is topspin. Slice causes the ball to hit the ground, stay low, and curve (kick) to the left. Topspin serves tend to hit the ground, bounce high, and kick to the right (opposite for lefty players).
1. The continental grip is only grip that will produce topspin on the serve.
2. The ball toss must be slightly behind the head. This will be an uncomfortable feeling at first, but the only way to add topspin is to keep your toss slightly behind you (thus forcing a slight bend in the back).
3. Hit from underneath the ball. Another way to say this is to hit the “brush the back of the ball” at contact. This will produce the topspin each player greatly desires. The key to adding topspin to a ball is to force the ball to spin over the top of itself.
4. Swing upwards hard and fast. The harder you swing, the more spin the ball will have (remember this may sacrifice consistency in the beginning).
5. Aim to the right of the service box (for a righty). Slice forces the ball to spin in towards the left. Depending on how hard you serve and how much slice you are hitting will depend on how far left you need to aim. If the ball lands to the left of the box, simply aim further to the right. After time, you will understand how to control the spin and be able to aim closer to the box.
6. Follow through may remain the same (across the body).
Important note:
Notice the way the ball bounces off of the ground. If the ball stays low, you are not hitting the ball correctly (for topspin). If the ball bounces up high or to the right (left for a lefty) you are on your way to a successful second serve