To support a broken arm in a sling, pull the sleeve until it fits snugly on the arm and elbow, then fasten the strap around the neck so the forearm and wrist are level with the elbow, as instructed by About.com. Keep all arm and shoulder muscles relaxed.
When putting on the sleeve, pull it over the forearm until the hand is at the end of the sleeve, but ensure it is not cutting into the hand or wrist, advises About.com. Reach with the other hand to grab the strap, and wrap it around the neck, firmly attaching the other end to the loop near the hand. Adjusting the strap until the arm rests at a 90-degree angle with the elbow helps to prevent blood from pooling in the hand. If the sling is attached too tightly, it can prevent blood from circulating, causing swelling, tingling, numbness, or discoloration of the hands and fingers.
If the sling has a back strap, grab it and tighten it around the back, ensuring it is not too tight by placing two or three fingers between the strap and your body, as instructed by About.com. Ask your doctor or physical therapist whether daily pendulum exercises for mobility are safe for your condition.