Bike cops have it worked out to a science:
http://www.ipmba.org/newsletter-0206-falling.htm
One of their drills is to have the cops ride in a circle while someone actively pushes them over. Basically, people get broken collar bones because they put a hand out. Don't do that. Look at photos of pros after they've fallen badly. Where's the blood? On their hips. Hip takes the fall first, then the shoulder. Hands on the bars, except you'll have to take the hand off the down hood. Practice it mentally while you ride. You'll activate mirror neurons, which will make it automatic when you do fall. This works. If I'm in a flat skid, I'll push the side of my helmet down into the pavement to take pressure off the down arm and shoulder.