Toes To Bar

Hanging from the bar, engage your whole upper body (as opposed to a 'dead' hang). This will also help you stop swinging. Hinging at the hips, raise your legs so that your toes come as close to the bar as possible. Bring the legs slowly down. Try not to swing - keep control the whole time.
If this exercise is too much, try a Hanging Leg Raise or Hanging Knee Raise.