Unfortunately we live in a time when people have come to the conclusion that the only way to get what they want or to get even is to not only shoot the person(s) they're mad at but everybody else around them as well. It is happening more and more and will continue to happen until we armed citizens get trained and take a stand against these evil people.
There's a few things we can do to be prepared for such an instance out in our everyday lives. This applies to most everywhere we would be daily. However, churches and schools will be a bit different due to the number of people especially kids. There are a few rules or guidelines we can go by to help us to survive this type of situation.
Rule #1 is that there are no rules when it comes to an active shooter. Active shooters are unpredictable. They have no stereotypical dress, race, looks, or behaviors that you can look at someone and say this person is about to shoot the place up. The one thing they have had in common is that they were mostly males.
When I worked loss prevention we had certain looks and especially behaviors we would watch to know someone was about to steel something. They would get fidgety, nervous, maybe sweat on forehead, and would always start looking around at people and cameras. Active shooters don't display the same signs so they're harder to pick out. If you see a person walk into a store with a trench coat on in the middle of summer you will want to keep your eye's on them. If you see someone walking stiff legged into a store or wearing long sleeves and is stiff armed you'll want to check them out to see if it's a medical condition or they have a rifle or shotgun hidden down their pants leg or up their sleeve. Someone dressed in "tactical" clothes with a backpack on especially if the backpack is on their front, you need to pay attention to them. If you see someone start putting earplugs in take cover or run. They're a few signs but these signs are unfortunately usually either last second or are no different than many of the people out there just going about their everyday life.
Most of the active shooters so far have all been different in the way they look, dress, act, and their race. Most of them someone at the place they shot up knew them, or at least knew of them. The ones that can identify them are the ones that are closet to them, family and friends. They have all either displayed signs or made comments that people should have caught, or should have taken seriously.
If you see someone with a gun or you hear gun shots get out of the place running away from the person or shots and get out as fast as you can. If you see police entering the building put your hands in the air while moving towards them following their commands. Keep moving in the direction they came from because they have already cleared that area.
Once you get to a point and can call 911 do so. Give them as much info as you can. What was the shooter wearing, sex, race, height, weight, age, location, etc. Keep calm and give the 911 operator some good info so they can get police there to either stop them or more than likely to clear the building and clean up. In these situations police won't typically be there to help you. They will get there after all the damage is done and will only be able to clear the building and start their investigation.
If you can't get out safely find a good hiding spot to take cover in. A room you can either lock or barricade the door, turn off lights, cell phones, and keep quiet. Stay hidden in there until the police come around giving the all clear. Make sure they give some kind of code or ID to let you know it is the police.
Help out anybody who is disabled or elderly to either get out or hide out. Keep in mind someone that has a broke leg may need more help than someone that has been a paraplegic for 10 years. They are used to their situation but the one with a broke leg has only been on crutches for a week or so. Help them both if possible if not help the one needing it most.
Once you are out of the building DO NOT re-enter until the "all clear" is given by the police.
For most people this is going to be a last resort. Most people will not have the tools to take out an active shooter. However, as the last resort find a weapon, scissors, pen, pencil, stick, shovel, fire extinguisher, pocket book, keys, etc. Take cover, and when the shooter is in range hit them fast and violent. If possible you'll want more than one person and all of you will need to strike at the same time. One down tie them up and restrain them until police arrive to take over.
For those who are armed, willing, and capable to confront the attacker. Take cover, know your target and beyond, remain calm, don't rush your shot, making sure to act quickly with a well placed shot to the attackers center of mass. If there is more than one, make sure to be covered from both simply because you're probable going to get return fire from the one you don't shoot at or you miss. Once committed to engaging the shooter(s) there's no backing out so make sure you are in a position to be effective.
This is a simple set of guidelines to remember. We must also remember each active is different and has a plan. If they're 2 or more of them they may have one go in one way, fire a couple of rounds to basically get everybody to "heard" the other way where the other shooter is waiting to take out as many as they can. If you hide out and he finds you, do something. Don't just sit there, at least try to attack them. You're more than likely going to be shot. If they come into the room you're in there have been quite a few survivors that survived simply because they played dead. This is an option, make sure your body is lifeless and limp. Take slow shallow breaths, you can either close your eyes or leave them open making sure you're not moving them.