Here are a couple of resources on active shooter situations:

https://www.youtube.com/watch?v=eKyLxDv9C9U (good video other than the very poor use of cover shown between about 4:05 and 4:30)

http://emilms.fema.gov/IS907/

As Phaedrus says, situational awareness is crucial.

Like with many other potential emergencies, physical fitness can really pay off if something like this happens where you are.

If you do carry concealed please remember to train and practice. Concealed carriers should plan to be at the range at least monthly, if not more often, and should budget for a class at least annually. Competition can be really helpful, especially for a bit of simulated stress combined with drawing, movement, using cover, clearing malfunctions, and reloads. Those skills are perishable and hard to maintain from inside a range booth.

Quote:
playing hero in a situation like this would only cause more problems.


I respectfully disagree. There have been a number of active shooter situations in the USA that have been stopped by civilians carrying concealed. Also, "playing hero" is not how I would phrase it. I think I would say something closer to "saving lives."