If you see one robber, expect a second. If you see two robbers, expect a third.

Don't take action when there are people behind you that you cannot identify or control.

If you issue a verbal challenge, try to do so from a position of cover.

Make sure you're not holding a weapon when police arrive.

If you shoot a robber, seek immediate medical attention for him.

Remember that the recording of your 911 call is available to lawyers of the guy you shot. Don't say anything you don't want repeated in the courtroom.

Don't chase after a robber. You move from self defense to an attempted citizens' arrest, a very shaky area of law.

Don't make citizens' arrest.

You are responsible for innocent bystanders you may accidentally injure.

I could go on and on.