On your side position your elbow under your shoulder.
Straighten your body and hold.
Hold for the desired amount of time.
Positioning elbow too far up.
Hips caving down.
Torso not being straight.
Hang from the bar with an overhand grip, spaced just wider than shoulder width.
Bring your legs up to be level with the hips.
Slowly lower back to the start position and repeat.
Swinging around.
Using momentum to kick legs up.
Dropping on the way down.