Hold the ball carefully.
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Although it may seem negligible, the way a player holds the ball before the toss is often why a serve goes awry. When the ball is tossed from the palm of the hand, the wrist comes into play, causing the ball to spin and swerve. The ideal flight path of the toss is straight up and down, like an elevator shaft.

To get the straightest toss, Williams says, hold the ball in your fingertips as if it were the bottom of an ice cream cone. "You're holding it in your tips, so as you toss up, the only thing you can do is release it and it goes straight up. It literally goes into the right spot."