Lean into the Ball

The balance of the body needs to be perpendicular to the direction of force otherwise the hands take the full brunt of responsibility to control the height of the ball. In other words, the hand can direct the height better if it follows the trajectory of the arm and the arm can follow the path if the trunk mass is moving around the same height line. The shin bone is connected to the thigh bone etc.
Good technique at contact has the natural appearance of falling through space as if in a state of rest on completion of what is and the beginning of what isn’t.

Keep Your Head Down

The shape of the chest at contact is hugely governed by the head and if the head is facing down instead of the court then the height is misjudged. Stiff neck pain is easily diagnosed. Since the ball comes in and out of contact so quickly, to follow the ball and the opponent, you need to bring the head in advance of the ball and therefore imagination must be used for micro-seconds. Players who stare down at the ball are left with their head staring at the empty space left by the ball while their opponent wins the point. Tennis must be played in advance to anticipate ahead, like chess and each shot involves a clever transition of one future to another. Players that are caught in the present are, in fact, swallowed by the past.