Crash tips?

Don't land with all your weight on your forearm because this is the result:
Apparently your forearm is susceptible to the common boxing injury, if you compress the tissue against the bone, it WILL burst open.

^ for the record, falling on your elbows is a hell of a lot better than landing on your hands (broken wrists likely)

rugby, judo and snowboarding are all good for learning how to fall properly

^+1 also skateboarding - this one gets you used to taking falls on tarmac/concrete which the above lack.

Although it all happens so fast, if you fall down a lot doing it right becomes instinctual... or you break a lot of bones. One of those.