Try a whip kick

Keep your legs held tightly together from your hips to your knees, and from your knees to your ankles. Bend your knees so that your shins come up to about a 90-degree angle, then quickly bring your shins apart and move them in a circular motion, keeping your thighs together the whole time. Bring your shins back together at the bottom of the circle, and lift them up again to restart the kick.