1. COVER NO MORE THAN HALF THE SHARP
Find “that perfect spot” where the sharp fits securely under the foot. For most people it is slightly forward of the ball of the foot, at the point where the big toe meets the ball. If you cover too much of the sharp, you risk playing other keys since the foot becomes wider at the contact point.
In addition, it requires several more inches to move from the natural to the sharp if you cover more than half the sharp. Economy of motion is particularly important when the motion is repeated frequently, such as when moving back and forth between naturals and sharps.