I personally have not intention of being the superhero at a shooting scene. I'm armed as a final option if/when an armed retreat is necessary--I have myself been in the position of pleading "please don't shoot me," and that is a position that sucks. I want a better option than that. I'm covering my wife as she escapes, if the shooter should be paying attention to us.
There certainly are some tactics discussed and trained for armed civilians. One, for instance, is to be the first person to call 911...because the first person to call 911 gets "victim" status. The second is to stay on the line and continually talking with 911 until the police have actually identified you as non-hostile.
Of course, there are other things, such as not having a gun in your hand as the police get to the scene. These kinds of things have to be thought about, trained, made mental rules.