Marine Corps Rules:

1. Be courteous to everyone, friendly to no one.
2. Decide to be aggressive enough, quickly enough.
3. Have a plan.
4. Have a back-up plan, because the first one probably won't work.
5. Be polite. Be professional. But, have a plan to kill everyone you meet.
6. Do not attend a gunfight with a handgun whose caliber does not start with a "4."
7. Anything worth shooting is worth shooting twice. Ammo is cheap. Life is expensive.
8. Move away from your attacker. Distance is your friend. (Lateral & diagonal preferred.)
9. Use cover or concealment as much as possible.
10. Flank your adversary when possible. Protect yours.
11. Always cheat; always win. The only unfair fight is the one you lose.
12. In ten years nobody will remember the details of caliber, stance, or tactics. They will only remember who lived.
13. If you are not shooting, you should be communicating your intention to shoot...