Lie on your back with your legs bent and knees together, hands under your butt. Tuck your tailbone and make sure your back is completely flat against the floor.
Lift your feet off the floor, raising them until your thighs are vertical and perpendicular to the ground. Keep your core braced and your knees bent at 90 degrees throughout the movement.
Bring your knees as close to your face as you can comfortably go without lifting your mid-back off the ground. Your hips and lower back should lift slightly off the ground.
Hold for a second, then lower your feet back to the ground with control, keeping your knees bent the whole time.