There are 4 universal rules of firearm safety.
1. Treat all guns as if they are loaded.
2. Never let the muzzle of the gun point at anything you're not willing to destroy.
3. Keep your finger off the trigger until the sights are aligned, and you're ready to fire.
4. Be aware of your target, what's in front AND behind.
The NRA teaches 3 fundamental rules.
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.
Any ONE of these rules can save your life or the life of another. Ignoring ANY of these rules will guarantee an accident waiting to happen.
Case in point.
Last month, one of my fellow NRA instructors had a student that had a little trouble with "keep the finger off the trigger". After repeated warnings he had to dismiss the student on the grounds of safety. It has had, as the student was one of his co-workers. :)
Saturday, that same student shot himself in the leg, while trying to holster his firearm... with his finger in the trigger guard. The hollow point bullet ripped through the middle of his right thigh and down to his ankle. It severed the femoral artery and he nearly bled to death. He was lucky to have someone at home and called 911. He had to get AirEvac'd to the hospital.
Follow the rules. Be safe.
Especially those of you who choose a Glock, XD or any other firearm that incorporates the safety into the trigger.