Pull ups are one of the most effective workouts in gaining upper body strength because it requires lifting the dead weight of your body using only your upper body. A pull up bar should be at a level in which you have to jump and hold the bar so that your legs and feet are not touching the ground, providing a mandatory dead weight lift.
To perform this exercise, first jump and maintain a grip on the pull up bar; be sure your palms are facing in the opposite direction of your face. To assist in balancing your body, cross your ankles and slightly bend your knees. Next, pull your body upwards until the pull up bar is on the same level as chin. Then, lower your body back to the starting position, making sure your elbows lower to a straight position. Repeat the process, without over-straining yourself, and keep from touching the floor each time you attempt another pull up.