Sooner or later it happens; flashing red and blue lights in the rearview mirror, a guy in a uniform strolls up to the car window, introduces himself and asks for a license and registration.

A traffic stop generally happens for one or more of these four reasons:

The driver and one or more passengers look like a suspect.

If there has been a crime and one or more of the passengers looks like the perp, the police may pull the car over and ask for identification and other related questions.

The driver disobeyed a traffic law

Talking on a cell phone and driving is not illegal. Distracted driving is illegal.

Traffic citations are a common reason police pull a car over. No, police do not have traffic citation quotas, however, anyone who drives is well aware that traffic violations exist and a cop who habitually ignores them will soon come under the ire of management and fellow police officers for failing to perform.

There is a problem with the vehicle or driver.

If there is a tail light out or the license tag appears to be missing, the police may stop the car. They will also stop a car if it seems to be weaving or driving erratically, such as what one would expect if the driver was drunk or having a heart attack.

The driver may have witnessed something

Sometimes, a driver or passenger will see something, possibly without being aware of it. In this case, an officer will stop the car and ask.

Things a driver can do to make the stop go smoothly

You want them to have your back but not be on your tail.

Pull over to a safe spot and stay in the car. The driver's hands should remain on the steering wheel. Passengers should stay calm.
Allow the officer to introduce himself and state the reason the vehicle was stopped. This should always be the case.
Wait until the officer asks for documents and mention where those documents are before reaching for them. Move slowly. Police work is hazardous and quick movements could be misinterpreted.
The law under ARS 13-3102, states that any person carrying a concealed firearm must acknowledge and comply with the demands of a law enforcement officer when asked if he/she is carrying a concealed deadly weapon if the officer has initiated an "investigation" such as a traffic stop. During the stop, the law enforcement officer may take temporary custody of the firearm for the duration of that contact for officer safety purposes.
If you are issued a ticket and are unsure as to the reason, ask for clarification without arguing. Arguments are not useful, helpful, or worthwhile. That is the reason for court.
Treat the officer in a manner which is consistent with your best personality traits, such as cooperation, honesty, and courtesy. Invariably, cops deal with a lot of argumentative, lying, grumpy people. Don’t be that guy.

Signing a ticket is not an admission of guilt. It’s a promise to either appear in court or pay the fine.