1. Lie on the floor and place hands on the floor or behind the head. 2. Bring the knees in towards the chest until they're bent to 90 degrees, with feet together or crossed. 3. Contract the abs to curl the hips off the floor, reaching the legs up towards the ceiling. 4. Lower and repeat for 12-16 reps. 5. It's a very small movement, so try to use your abs to lift your hips rather than swinging your legs and creating momentum.