I find it helps if you're pished when you fall over
Seriously though, it helps if you can fight the instinct to tense up. Relax and go with it and you're more likely to bend than break.
Same is true when you bin it (always helps if this is on a track though and you don't have cars to hit), what is it that Keith Code says "if you're not prepared to fall off then don't get on a motorcycle", or words to that effect, "but if you do fall off, try and relax and let a lot of your leathers take a little bit of a beating rather than a little bit of you leathers taking a lot"