Calf Raises

"You should do calf raises standing on a book, only now your toes should be elevated so they are higher than your heels. Hold the back of a chair lightly for balance.Your feet should be parallel and a few inches apart. Lower your heels to the floor, stretching the calf muscle, and then raise all the way up on your toes." (Arnold: The Education of a Bodybuilder p. 171)

Modifications:
To increase the intensity, increase the weight by using dumbbells.