The Move: 2nd-Position Plié
You'll quickly feel this in the seat and the thighs, but to maximize the stomach-flattening, focus on keeping the abdominal muscles engaged, says Williams.
1. Step your feet two and a half feet apart (or wider than your hips) and turn out your toes.
2. Place your hands on your hips and roll your shoulders back.
3. Bend your knees until your thighs are parallel to the floor.
4. Tuck your tailbone under and pull the abs in and up, tracing the letter "L" with your belly button.
5. Pulse down one inch, up one inch (that's one rep). Keep the moves small and controlled and the back straight and tall.
Bonus: Lift one heel up a few inches for two counts, then lower and lift the other heel.