Nice article!
In addition to The 4 Rules,
I have 2 more:
#5 Everyone stands behind the person shooting, unless one is standing beside the shooter, and even then a step behind is a good idea.
#6 When carrying a pistol or revolver, especially concealed, always use a holster that completely covers the trigger.
And while this is not worthy of rule status, retention holsters can be very dangerous, especially if they require you to do some kind of manipulation with your trigger finger in order to release the firearm from the trigger.
An IWB holster and a good belt give me all the retention I need.
Personally, I don't need a retention holster except on days when I spend a significant portion of the day hanging upside down, and I do all I can to avoid such days!
However, other people, of course, have different needs.