Sit on the bench with your knees bent. Your feet should be on the inclined side of the bench. Hook your legs under the foot brace or support bar. Lie down so that your upper body is declined, place your hands behind your neck, or cross them over your chest. Raise yourself from the bench, make sure your abs stay tightened and your back is straight. You should raise up until your upper body is completely vertical. Lower yourself down slowly until the back of your shoulders touch the incline board. Keep your back straight and your abs tight. For a more challenging sit up, you can hold a weight against your chest, with your arms crossed over top of it.