The serve is a critical shot in tennis and the only shot that you fully control. In other words, since you initiate the serve, you don't have to prepare for an incoming ball from your opponent. In order to hit a good serve, however, you need to toss the ball properly because your swing will be determined by where you place your toss.

In order to make a good toss, the ball needs to be held on the fingertips. The palm should face directly toward the sky as the arm goes up and the ball should be pushed into the air using the straight forward and up technique. These factors help to limit spin on the ball and enhance overall control of the toss. The tossing arm should go up and out to the side of the body assisting trunk and shoulder rotation. The weight starts to move forward as the arm moves upward.

Video:  The Ball Toss
In this video clip USPTA Master Professional Rick Macci explains the ball toss and where it should be released in relation to the player's body in order to hit successful serves.
Source: USPTA Tennis Tip of the Week

Shot fundamentals involve all of the skills and techniques necessary to properly execute a sound stroke, from preparation to finishing of the shot. This week's tip refers to two important fundamentals: the backswing and the follow-through. USPTA.

Professional Brett Hobden breaks the swings into five segments each: five parts on the backswing and five parts on the follow-through, five being the longest backswing and longest follow-through. He explains that the segmented swing is a great way to illustrate how much backswing and follow-through is needed for control. For example, a player will be using a five-five swing to hit a groundstroke, which means five parts backswing and a five parts follow-through, whereas a two-two swing will be used for a drop shot. The video provides a visual representation, which helps you understand the concept.

Video:  The segmented swing              

Brett Hobden explains the concept of the segmented swing and illustrates how much backswing and how much follow-through is needed for certain shots to control the ball.

Source: USPTA Tennis Tip of the Week