From Jeff Cooper,
A pure slice serve has nothing but sidespin, but most slice serves also have some topspin or, more rarely, backspin.
Topspin-slice serves are often called slice serves, and while there's no sharp line between the two, a serve that is at least 75% sidespin behaves differently enough to deserve the distinctive name . Between 100% topspin and 100% sidespin, any mixture of the two spins can be created. The higher the percentage of sidespin, the lower the bounce and the sharper the curve to the left (from a right-handed server). The extreme slice serve often has some backspin, which further accentuates the low bounce and the leftward curve.
The serve shown here is a pretty heavy slice, having at least 90% sidespin. It would be used primarily as a first serve, because the lack of significant topspin gives it a low margin of error over the net. This serve will pull the receiver wide, opening up the court, and often stretch her too far to hit a solid return. On the ad side in doubles, it can pull the receiver far enough onto the deuce side so that her opponent blocks some of her placement options. If you place a slice slightly to the right-handed receiver's backhand, it will curve into his body to "jam" him.
Key points: Aspects of the toss and windup that are the same as for the topspin-slice serve are covered in more detail in that video lesson.
* Stance: Stand with your right foot parallel to the baseline and your left foot pointing roughly toward the right net post.
* Grip: Use a Continental grip, holding the racquet loosely enough that it will pivot in your hand as you close your outer fingers just before meeting the ball.
* Toss: Toss the ball lower and farther to your right than on your topspin/slice serve and barely forward at all.
* Wind-up: Use your normal wind-up.
* Swing: Use some upward thrust from your legs as you would on any serve, but don't lean into the court.
You'll generate enough forward force through the turning that begins at your feet and continues through your legs and upper body into the rightward swing of your arm.
* Point of contact: Meet the ball 1-2 feet below the full upward extension of your reach, roughly 2 feet to your right, and barely in front of yourself, as measured by where your head is at the time of contact.
* Striking the ball: To hit pure slice, try to brush across the right side of the ball, at what would be 3:00 on its face if it were a clock. Your racquet face will naturally turn toward the net and brush across the back of the ball from its center outward toward that 3:00 point, making the ball spin around a vertical axis, like a perfectly balanced top. If you keep your wrist too tight and force the racquet to stay in its initial edge-forward position, you will hit the ball much too far to your left (if at all).
* Follow-through: Follow through to the left side of your body (for right-handers). You won't step into the court nearly as much as on the typical topspin-slice serve.