How in WII tennis do you serve hard?

Make a fast, quick move moving you wrist down hard. The most important thing is to do the action with you wrist correctly. From a position with the Wiimote pointing forwards and up, press A to lob the ball, and then, when you need to hit, move your wrist so it will point front and down, fast and strong. It should work.

How to do a very hard, fast serve in Wii tennis, you basically have to hit the ball at the right time- when it is at its peak in midair. It takes a little bit of practice. Look at the service line and when you see the ball reach it, that is when you swing.