Of the two most widely accepted sets of gun safety rules, that being the “Fundamental NRA Rules of Safe Gun Handling”, and the “Four Rules of Gun Safety, by Jeff Cooper”, I prefer the Jeff Cooper rules, and I might be getting picky here but, with a few modifications.

Below are two of the most widely accepted sets of gun safety rules

“Fundamental NRA Rule of Safe Gun Handling”

1 Always keep the gun pointed in a safe direction.
2 Always keep your finger off the trigger until ready to shoot.
3 Always keep the gun unloaded until ready to use.

(although good rules to live by, they just seem a little inadequate to me)

“Four Rules of Gun Safety, by Jeff Cooper”

1 All guns are always loaded. (all guns are not always loaded, although you should “treat” them as such)

(I reverse 2 and 3 because I believe you should be thinking about keeping your finger off the trigger before you ever have the opportunity to muzzle anyone)
2 Never let the muzzle cover anything you are not willing to destroy.

3 Keep your finger off the trigger until your sights are on the target. (if you want to hit your target quickly, you need to have your finger on the trigger and the slack taken out by the time your sights are on the target)

4 Be sure of your target and what is beyond it. (not just beyond it, but all around it. Could there be something beside your target, or that could come between you and your target, that you would not want to shoot?)

The “Four Universal Firearm Safety Rules” I live by and impress upon new shooters are:

1 Treat all firearms as though they are loaded.
2 Keep your finger off the trigger until your pointing in and ready to shoot.
3 Never let the muzzle cover anything you are not willing to destroy.
4 Be sure of your target and what is around it.