Sit on the ground with your legs stretched out in front of you, feet together. Place the resistance band below the center of your feet, and pull it up far enough to take out the slack.
Lean backward enough to engage your abdominals, bringing your heels up off the ground and pulling the band up toward your chest; your palms should be facing each other with your hands close together.
Rotate your torso from side to side, trying to bring the resistance band as close to the ground as possible with each rep.