Before hitting the ball, use the D-Pad and press:
Up: To produce a shot with little distance or power.
Right: To hit the ball to the right side of the screen.
Down: To produce a shot with long distance and power.
Left: To hit the ball to the left side of the screen.
You can also use combinations such as Left + Down, etc.
You will find it much easier to return opposition serves if you stand up closer to the net. This greatly increases the chance of you returning the serve. Against players who serve slower, you will not have to resort to doing this.
When you start the game, go to 'create'. From there, make three characters and put them into the group. Take the new characters' gold, weapons, and armor, and give them to the old character, then save. Restart the game and erase the new characters. Repeat until you're filthy rich.