Come to a forearm plank; pull your navel toward your spine, and tuck your hips under to find a perfect plank position. Make sure your neck is in line with the spine for proper form.
Alternate dipping the hips side to side in a slow, controlled motion. Rotate your hips until they are one inch off the ground on either side as you dip. Think about arching the hips like a rainbow when moving from side to side (think up and over).