The Inside Crescent Kick should be performed much like the Front Stretch Kick. The same "back straight and arms out" posture is assumed. You once again step out with one leg first then kick with the other. The circles should be big and round like a nice rainbow going across your face.
Slap the balls of your foot with your hands. This means you have to turn your foot inwards so the the soles of your foot and the ball of your foot faces the inside of your body.
*Tip - When slapping the foot, bring your foot to your hands and not your hands to your feet. Also, do not drop your hands or let them swing around and flap like wings. Your arms should be still and immovable.