To perform hanging leg raises use a pull-up/chin-up bar or some other device which allows your alleviate yourself in the air. With your knees slightly bent raise your legs off the floor towards your chest making sure to keep the tension on your lower abs. As your knees come towards your chest your pelvis should rock slightly forward. Lower your legs down slowly in a controlled manner. Do not place your feet on the floor, keep them above the ground. Repeat the process.