Jeff Cooper's Commentaries: Vol. 6, No. 2:
ALL GUNS ARE ALWAYS LOADED
The only exception to this occurs when one has a weapon in his hands and he has personally unloaded it for checking. As soon as he puts it down, Rule 1 applies again.
NEVER LET THE MUZZLE COVER ANYTHING YOU ARE NOT PREPARED TO DESTROY
You may not wish to destroy it, but you must be clear in your mind that you are quite ready to if you let that muzzle cover the target. To allow a firearm to point at another human being is a deadly threat, and should always be treated as such.
KEEP YOUR FINGER OFF THE TRIGGER TIL YOUR SIGHTS ARE ON THE TARGET
This we call the Golden Rule because its violation is responsible for about 80 percent of the firearms disasters we read about.
BE SURE OF YOUR TARGET
You never shoot at anything until you have positively identified it. You never fire at a shadow, or a sound, or a suspected presence. You shoot only when you know absolutely what you are shooting at and what is beyond it."