1. Every gun is loaded.
2. Never cover anything with the muzzle you aren't willing to destroy.
3. Finger off the trigger until you've sighted on your target and are ready to fire.
4. Identify your target and background before you shoot.
Seems like common sense, but I was shooting under supervision at a young age and grew up with these rules. I'm amazed how many otherwise rational adults don't understand the responsibility that comes with touching a gun and will do potentially deadly stuff like point the gun at others.
I do have to admit I violate those rules at times. I like single action army style cowboy revolvers and have even learned to twirl them. That means violating those rules repeatedly, but whenever I pick up one I treat it as loaded until I confirm it is not. And if I set it down or holster it I check it again just to make sure.
A lot of firearm safety is mental training and familiarity with your gun, but those four rules will never let your down. I also liked the next video on gun condition of readiness. Point is to know your chosen weapon and exactly how to safely operate it. And if you decide to carry for self-defense you must educate yourself on when it's legal to shoot and, even more important IMHO, to learn how to avoid potentially dangerous situation where you may have to use your weapon.
But I find it hypocritical when some call us gun nuts because we train with our guns so we can use them safely. HOAs hold disaster preparedness classes and TV commercials tell us to have a home evacuation plan in case of disaster, and owning a fire extinguishers are common sense, but if we have a plan for how we would deal with a home invader then we are again crazy gun nuts with a thirst to kill.
Sorry for getting political.