These are simple tips to improve your forehand shot in tennis:
– generate power with rotation and arm extension through the contact zone
– generate topspin by using your legs and moving upwards all "levers" in your arm
It's best if you can first isolate each movement in order to become more aware of it. Then try to put them together and create a smooth and effortless movement that will create power and topspin on your tennis forehand groundstroke.