Originally Posted by TheCheese
Do you have any insight into how to teach someone to be able to curve the ball left-right or right-left like Federer is able to do? (He'll commonly have to ball curve to the right on an inside out forehand, for example)
Brushing the ball across will lead to that famous inside out left to right curve. There is also an upward component, but just dropping the racquet below the ball to approach it and pulling the racquet towards you and the finish will naturally induce the windshield wiper lift as well.