How about 7 rules?
If there is going to be a gunfight
1: Be somewhere else
2: Have a gun. A gun that works and you know how to use.
3: A rifle is better than a pistol
4: Bring a friend, have him bring his rifle.
5: Know the difference between cover and concealment
6: Stay behind cover as much as possible.
7: First guy to die, looses.
Stopping power: The power some guns have to make you stop what you are doing and get your wallet out.