If your just laying the bike down on it's side, like in a slick turn or such, keep your hands on the bars and let the bike take the impact. You'll have a very very strong instinct, almost unconscious, to put your arm down as you go down, but you need to just fight it. This is how I broke my wrist. It's better to have a ton of road rash than to have a broken wrist AND road rash.