These videos show some good ones but you have to look for them in the videos, just like you do in real life. Watch the videos and see if you notice the following things to watch for and to do/not do.
Note: you have to click on the first link to see it.
Step back out of arms reach
don't look away form the person
don't allow yourself to be surrounded
watch their eyes: sometimes they will look away, sometimes they will stare at you intently
watch their hips for shifts or balance changes
watch their shoulders for shifts and unleveling
Watch their hands for clenching, extreme hand position changes - raising or lowering