Warrior Poet Society discusses the universal firearm safety rules in this YouTube video. Proper safety includes following the rules, practicing the rules, and considering enrolling in gun classes. There are four universal rules.
Always treat the firearm as loaded and always know the gun’s condition.
There is no exception to this. Even after a person has cleared the weapon’s chamber and hands it to another person for inspection, the person who takes it automatically treats it as though it’s loaded during handling. Knowing the condition of the firearm includes knowing when there is a round in the chamber, if there are any left in the magazine, and when it was last cleaned. If the firearm is not in a holster, it needs to be cleared with the slide back in the locked position.
Keep the finger off the trigger until the sights have been aligned and the decision to shoot has been made. Fingers can accidentally twitch, potentially pulling a trigger back and causing disastrous consequences.
Never point a firearm at anything that is not intended to be destroyed. Understanding this means never pointing the gun at anyone or anything unless there is a clear intent to shoot. Never allow the muzzle to cross the flesh of any person.
Thoroughly know the target, what is in front of it, behind it, and both the left and the right. If these things are unknown, a person should not discharge their firearm.