That's what the helmet is for! ;-)

I used to reach out my hands when falling, but now I tuck them in and lead with my shoulder. that was my first major fall, but it's something that I would repeat to myself in my head while riding. In the aforementioned case, I was falling sideways and forwards. I suppose if I were leading with my head I would try to break the fall with my hands. I don't know; it all comes down to muscle memory, subliminal reaction, and how bad I'm freaking out at the time.