Keep This in Mind

You can instruct someone in the concepts of firearm safety, and "best practices", but unfortunately, this is a skill that has as much intrinsic knowledge, as taught. If you don't know, it is certainly essential to take a basic course in the mechanics of the firearm you are using -- but after this, do not assume you are an expert.

BASICS
1. The firearm is always loaded. Even if you know it is not loaded. It is guaranteed you will have an accidental discharge if you assume the firearm is unloaded.
2. Never point a firearm at anyone, ever. Unless you are going to shoot them. Always know where your firearm is pointed, at all times. The firearm's barrel reference point should NEVER travel in line with anything you are not going to shoot.
3. It isn't the cost of the gun, that sets you back monetarily. It is the cost of the ammunition.
4. If you like to go shooting, you'll spend more time loading clips, than shooting. Go figure.
5. If it is hard, and flat, and you shoot at it, the bullets will come back at you.
6. The interior of a car is designed to tumble bullets back at the shooter.
7. The M16 (and variations of it) is a piece of crap, the AK47 will never let you down.
8. Use non-corrosive ammunition. Clean your firearms when you are done shooting, every time.
9. If you do not protect your hearing, you will go deaf.
10. A spent bullet can travel several miles, so be careful where and how you send off rounds.

BONUS POINTS
11. Always err on the side of caution.
12. If it might be dangerous to shoot at, don't.
13. Don't get cocky. A firearm is not a toy. It is very dangerous.