How to react to active shooter situation

The U.S. Department of Homeland Security offers the following information on how to deal with an active shooter situation:

Active shooter situations are unpredictable and evolve quickly. Typically, the immediate deployment of law enforcement is required to stop the shooting and reduce harm to victims.
Because active shooter situations are often over within 10 to 15 minutes, individuals must be prepared both mentally and physically to deal with an active shooter situation.
Be aware of your environment and any possible dangers.
Take note of the two nearest exits in any facility you visit.
If you are in an office, stay there and secure the door.
If you are in a hallway, get into a room and secure the door.
As a last resort, attempt to take the active shooter down. When the shooter is at close range and you cannot flee, your chance of survival is much greater if you try to incapacitate him/her.
Call 911 when it is safe to do so.

The department also said there are three ways to respond when an active shooter is in you vicinity:

Run: Have an escape route and plan in mind, leave belongings behind, keep your hands visible.
Hide: Hide in area out of active shooter's view and block entry to your hiding place and lock doors.
Fight: As last resort and only when your life is in imminent danger, attempt to incapacitate the active shooter, throw items at the active shooter.

Once law enforcement arrives of the scene the department offers the following information:

Remain calm and follow officers' instructions
Raise hands and spread fingers
Keep hands visible
Avoid quick movements toward officers such as attempting to hold on to them for safety
Avoid pointing, screaming and/or yelling
Do not stop to ask officers for help or direction when evacuating, just proceed in the direction from which officers are entering the premises

Information to provide 911 operators: