The forehand is probably the easiest tennis stroke. It is very straight forward in the way you hit it. Technique is shown in the picture below.

Position of your upper body is very important. In Picture 1, the player is sideways to the ball, so he can rotate his body with the motion of his racket. Also, notice how he is leaned back in the first picture, so he can lean forward into the shot to put more power on it and have more stability.