A tennis racket must accelerate through the ball in order to make a good stroke. The head must stay stable with the eyes on the ball as contact is made and the racket (club) releases down the target line. Swinging too hard or out of balance will usually result in the ball going off line or potentially out of bounds. Body weight loads up on the right side on the back swing and to the left on the down swing, then completely left on the follow through.
The ball must be hit on the sweet spot, directly in the middle of the racket (club face). Rolling the racket from an open to a closed position through contact will result in a topspin shot (or a draw in golf). Keeping the wrist and hand firm through contact and not allowing it to close will result in a backspin shot (or a fade in golf). The racket (club shaft) should end up in a high position by the head at the end of the follow through.
Many ball sports have lots of similarities to golf from a co ordination / balance / agility point of view, however working with a good tennis player vice versa has a quicker impact of their golf development.