In civilian circles a firefight is known as a gunfight, so quite naturally the very first and most important rule when going to a gunfight are:
1. Have a gun. 1.1 Preferably, have at least two guns.
All additional rules are supplemental to that first rule.
2. Bring all of your friends who have guns. 2.1 Preferably, they will all have at least two guns.
3. Anything worth shooting is worth shooting twice. 3.1 Ammo is cheap. Life is expensive. 3.2 There's no additional paperwork for shooting someone more than once. 3.3 Two in the chest, one in the head is not a bad plan
4. Only hits count. 4.1 The only thing worse than a miss is a slow miss.
5. If your shooting stance is good, you're probably not moving fast enough or using cover correctly.
6. In ten years nobody will remember the details of caliber, stance or tactics. 6.1 They will remember who lived.
7. Proximity negates skill. Distance is your friend. 7.1 Lateral and diagonal movements are preferred.
8. If you are not shooting, you should be doing something else. 8.1 Communicating, reloading or running are the preferred things.
9. Accuracy is relative: most combat shooting standards will be more dependent on the "pucker factor" than on the inherent accuracy of the gun. 9.1 Use a gun that works every time. 9.2 All skill is in vain when an Angel pisses in the flintlock of your musket.
10. Someday someone may kill you with your own gun. 10.1 If they do, they should have to beat you to death with it because it is empty.
11. Always cheat, always win.
11. Always cheat, always win. 11.1 The only unfair fight is the one you lose.
12. Have a plan. 12.1 Have a back-up plan, because the first one won't work. 12.2 If you find yourself in a fair fight, you didn't plan your mission properly.
13. Use cover or concealment as much as possible.
14. Flank your adversary when possible. 14.1 Protect your own flank.