When playing career mode, to beat the computers you should hit it back and forth from side to side using X or B. But, if you are going to play xbox live, then you will have to trick your human opponent by hittng it down the line 2 times when they expected you to hit it to the other side of the court. Or, if you can really see what your opponent is doing when your going to hit the ball, hit it to opposite side of where he is running to, or standing.