At least four people are dead and 14 others wounded after a gunman went on a shooting rampage in Northern California Tuesday.

Two children are among the injured.

It's not clear what the gunman's motive was, but neighbors had lodged complaints about him and he was the subject of a domestic violence call the day before the attack.

Here’s a look at experts’ advice on how best to deal with an active shooter situation.

What are the steps to take when there’s an active shooter?

In the event of an active shooter, the Advanced Law Enforcement Rapid Response Training Center says to avoid, deny and defend -- in that order, if possible.

First, Dr. Peter Blair, the executive director of ALERRT and a criminal justice professor at Texas State University, said people should avoid the attacker by creating an exit plan and moving away from the threat quickly.

The next option, Blair said, is to deny the shooter access to one’s location. That could include putting up barriers to block the shooter or turning off the lights.

And finally, as a last resort, one should defend against the attacker, Blair said. “Do not fight fairly. This is about survival,” ALERRT’s website said.

"The immediate goal should be: how do I become a harder target?"
— Greg Crane, founder and CEO of the Alice Training Institute

Blair told Fox News that it’s important for people to be prepared and have a “script” in mind for high-pressure situations.

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“When you walk into any location, locate the secondary exits,” Blair suggested. “Be aware so that you can avoid the crowds all leaving out the same main exit.”

Blair also encouraged people not to take lightly the feeling that something is wrong. For example, “if the concert music stops, start taking action,” Blair said.

What if the shooter is at a higher level?

Blair recognized there could be situations when not all of the three recommended steps are viable options, such as during the Las Vegas massacre in October. In instances when the shooter is at an elevated level, the only option people have is to avoid, Blair said.

In those types of situations, Alice Training Institute founder and CEO Greg Crane said people need to evacuate and make themselves less of a target.

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“The immediate goal should be: how do I become a harder target,” Crane said. For a shooter on a higher level, that could mean standing straight up instead of lying flat on the ground, Crane said.

Anything else to know?

When the police arrive, the University of Miami’s Miller School of Medicine encourages people to make sure hands are empty and visible. People should also follow officials’ instructions and avoid making quick movements.

Blair and Crane stressed the importance of recognizing the sound of gunshots.

“If you hear repeated loud banging, treat it as if it’s gunfire,” Blair said.