don't try and be a leader with a bunch of strangers unless the situation obviously presents itself. people are going to panic, act in their own way, scatter, not listen to you, etc. worry about yourself and your family unless you can save a life.
While it is difficult to anticipate ever scenario that could occur in general the above advice sounds pretty good.
A big concern for me is exactly how I handle my gun. Even if I’m not planning to engage the shooter I would want my gun in hand at the ready. However, as mentioned earlier what if another citizen or a LEO spots you after hearing the report of “Man with a gun” and engages you?