One of the most important aspects of a good serve is balance. In this frame Na Li has rocked off her front foot and her weight is transferring onto her back leg. The left arm is straight ensuring a consistent ball toss.

Key point: The fact we can see Li’s back in this shot shows that she starts the serve side-on, a basis for good trunk rotation in the serve.

As the ball reaches the highest point of the toss Li’s knees are bent in preparation to push upwards to maximise her height and meet the ball at as high a point as possible. Her body is perfect alignment.

Key point: Note how her shoulders have tilted slightly so she can get under the ball.

Her legs drive her upwards and forwards – she will land inside the court after contact. The racket head has dropped behind her back ready to accelerate up creating racquet head speed and her back is arched.

Look at how Li contacts the ball in the top third of the racket face. This is the absolute highest contact point within the sweet spot, giving her the feeling of serving down into the service box rather than pushing it over the net.

Key point: Keeping your eyes on the ball until the contact point is crucial to a good serve. Where the head goes, the body follows: if it drops, your body weight shifts forwards rather than upwards, dragging the serve down.

Li’s racket has continued along the path she wants the ball to travel and she hasn’t pulled it across her body too quickly. Her left arm swings across instead – it has played an important role in keeping her balanced.

Golden rule: Li’s perfect balance allows her to remain airborne a lot longer than other players, a sign she has really attacked the serve.