It's horrible that I have to do this nearly two decades after Columbine, but I added "When A Shooting Strikes" to the Tools section of my Columbine site.
(At the Columbine page, scroll down, or use its vertical menu):
I kept it simple:
1. What to do if you face a shooter. Run, Hide, Fight was popularized fairly recently, a wonderful development. It is simple and easy to teach kids. This is key, though:
Follow the steps in order: Only hide if it's impossible to run; only fight as a last resort.
There are some great videos, which I recommend. They flesh out the ideas and offer good examples, with visuals that you are can recall easily if the moment ever arises.
I also included the key points from the TSA's great active shooter pocket card, and a link to download the full card.
2. Interpreting media coverage: Most of us will never face a gunman, but we will be inundated by media reports. I wrote the Skeptic's Guide to Media Coverage of Mass Shootings for The New Republic in 2015, after one of these awful shootings, and some awful coverage.
3. What we can do: I've written a new epilogue for the expanded edition of Columbine, to address two key strategies to stop this blight. I summarize them, and link to a free excerpt from the new epilogue.