When doing this stretch it is important to remember that you are trying to lengthen the tendon, this is done without firing the muscle.
Slowly go down on one heel until you feel a stretch in you calf. Hold the stretch for 10 to 15 seconds then move your weight onto the other foot.
It is important not to go up on you heel as this fires the muscle.
Repeat this stretch 10 to 15 times 1st thing in the morning and last thing at night when the muscle is at the tightest.