The best advice I could give with the hand and arm movement is to get the ball in your hands and practice by cradling the ball. Don't release it, and you can do it at home, just pretend you are about to deliver the ball and practice swinging it back and forwards. In front of a full-length mirror helps as you can see your body position and swing-plane. The closer you can keep the ball in line with your front foot the better as it aids in balance at the foul line (stops you falling to one side), and also practice keeping your swing plane straight - less to go wrong at delivery that way.
Last but not least - remember that sometimes less is more. Parker Bohn III gave me that advice and it's very true. You don't have to try and throw a ton of revs at huge speed to score. It's all about getting in the pocket and carrying, not how fast or how many revs you can throw.