From a hang position, you will relax and let your bodyweight settle in. Once you reach a relaxed stretched position, you will perform a reverse shrug. Basically, try to keep your arms straight and pull your shoulder blades down. This will pull your body up.
One good tip is to try and keep your chin down. This will keep you from pulling into the start of a chin.
This is a great movement for shoulder injury prevention as well as bringing up the upper back region.
It does not take much to get the most out of this movement — 1 or 2 sets to failure seems to work best. I also have had great luck by having athletes hold the contracted state for a 2-count before returning to the start position.
