Lie on your back on the mat and keep your arms by your sides. Then, start bending your knees and place your feet on top of the ball. Make sure you have your heels together and toes pointing slightly outward in a small V shape. Keep your abs firm and contract your glutes to lift your hips an inch off the floor, then roll the ball away from you until your heels are on the ball. Then, bend your knees to roll the ball back to the starting position. Make about 20 reps of this exercises, always having your abs firm.