4 Common Sense Rules of Firearm Safety (My Version)
1. Treat ALL firearms as if they are ALWAYS loaded and ready to kill, maim or destroy.
This one seems to be pretty straightforward, but it is also the most important. How many times have you heard the old line "It just went off"! So no matter if you are at the range, home or getting ready to go out and you know your gun is unloaded, ALWAYS assume that it is loaded.
2. Keep your finger off the trigger until you are on target and ready to kill, maim or destroy.
You have probably all seen it a time or two; whether on the range or on T.V. someone is walking around carrying their gun with a finger on the trigger. This is a very Hollywood and unsafe practice. You should allow your finger to rest on the frame of the gun outside of the trigger guard until you are on target and ready to engage. This is a habit that you must get into; it is paramount that you follow this rule at all times, including while drawing or holstering your firearm. You do not want to be "that guy or gal" who accidentally shoots themselves while drawing or holstering their firearm.
3. Never cover or flag anything with your firearm that you are not willing to kill, maim or destroy.
This means never point the barrel (cover) anything with your firearm you do not wish to kill, maim or destroy, including oneself. This can get tricky depending on which carry method you use, including holster location and draw stroke. If you are not mindful of your barrel during holstering or drawing you could potentially be violating this rule on your own body. Also, if you use a horizontal carry shoulder holster realize that you are probably unintentionally covering many things that you do not intend to kill, maim or destroy. In some cases it is unavoidable; if you use an IWB holster you will inevitably cover some part of your body, and that is why Rule #2 is so important.
4. Be sure of the target that you are prepared to kill, maim or destroy AND what lies beyond.
Understanding and seeing what lies beyond your target is very important. The last thing you want to do is kill, maim or destroy something that you did not want to. You need to understand that a bullet does not just magically stop in your intended target. They have the ability to continue traveling great distances; possibly impacting another object or person. Not only do you need to worry about over penetration; there is also the chance of a complete "whiff" with a shot. Depending on state laws you could be charged with involuntary homicide and open yourself up to a civil case.
This is by no means the only common sense rules of firearm safety; to me, they are just the main and most important ones. Everyone will have their own opinion of the order of these 4 rules and that is fine; please feel free to comment.