Stumbled across this at first hilarious and then sobering how-to guide: How to: Survive a Riot
Let's hope we never need this information, but let's keep in mind:
If you fall down, pull yourself up into a ball. Protect your face and ears and internal organs. In this position you are a smaller object that can be avoided. You will receive less damage if you are stepped on. If others trip on you they will help create a larger "pile" that rioters will avoid.
Try to avoid looking conspicuously wealthy, as you are likely to draw the unwanted attention of opportunistic thieves.
Now you know!