1. Avoid the use of "policeman," "patrolman," "fireman," etc. The number of females in public safety professions has increased significantly in the last twenty years.
2. Don't assume your officers have partners. Virtually all police work is performed by officers assigned individually to one-officer patrol cars. There are exceptions, mostly in larger cities on the east and west coasts. Pairing officers or detectives as partners certainly increases opportunities for interaction and conversation but keep in mind that a formal, permanent partnership is unlikely in most police agencies.
3. Know your weapons. If your story includes firearms, know your subject before you make stupid mistakes like having a revolver eject empty shells onto the ground. Or inserting a "clip" into a pistol (it's called a "magazine.")
4. Check your terminology. There's a difference between burglary, robbery, and theft. Is drunk driving called DWI or DUI in the state where your story is set?
5. Tread carefully in the morass of legal procedure. Lots of room for mistakes here. For example, there's no requirement that officers give a suspect the Miranda warning at the time of arrest. It's usually done just prior to an interrogation. The convolutions in navigating the criminal justice system is dizzying even for those in law enforcement. Although you may want your bad guy arrested, tried, and convicted inside a week, he will attend a dozen or more court hearings between arrest and sentencing over the course of months or even years.
6. Give your police officers a life outside of work. We've read too many novels where officers seem to work 24/7 with no mention of family, leisure activities, or personal interests. Even diehard cops have to sleep, feed the dog, go to church, and check on the kids.
7. Avoid stereotypes. Not all police officers are alike. Beware giving your female MC the standard characterization of having to prove herself to her male counterparts, as well as to the world in general. It's a worn out story line and most police departments are way past that.
Great writing can overcome lapses in correct procedure and terminology without losing credibility when most of the story rings of authenticity. Breaking the rules doesn't take away from a story's authenticity when it is done sparingly and in a believable manner.