Whether or not this is correctly attributed, I am not sure. Regardless, it’s damn good advice.

Rules For A Gunfight by Drill Instructor Joe B. Fricks, USMC

1. Forget about knives, bats and fists. Bring a gun. Preferably, bring at least two guns. Bring all of your friends who have guns. Bring four times the ammunition you think you could ever need.
2. Anything worth shooting is worth shooting twice. Ammunition is cheap – life is expensive. If you shoot inside, buckshot is your friend. A new wall is cheap – funerals are expensive.
3. Only hits count. The only thing worse than a miss is a slow miss.
4. If your shooting stance is good, you’re probably not moving fast enough or using cover correctly.
5. Move away from your attacker and go to cover. Distance is your friend. (Bulletproof cover and diagonal or lateral movement are preferred.)
6. If you can choose what to bring to a gunfight, bring a semi or full-automatic long gun and a friend with a long gun.
7. In ten years nobody will remember the details of caliber, stance, or tactics. They will only remember who lived.