The most important bit is of course the four rules-
1. All guns are always loaded.
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.
4. Be sure of your target and what is beyond it.
If you don’t break them you will never put a bullet sized hole into anything you didn’t mean to shoot. If you break more than one at a time you are near guaranteed to have a negligent discharge and only luck will determine what happens then. It only takes a moment.