First and foremost: the police don’t talk to innocent people. If the police are talking to you, it already means they suspect you of committing a crime. They are simply looking for evidence or probable cause to arrest you at that point.
The police can detain you briefly without an arrest. Of course, anything you say will make that detention last longer. You may be required by law to identify yourself, so other than that don’t say a word!
The police will lie. Never trust anything a police officer says. Never. Under any circumstances. This is the God’s honest truth and the saddest part about living in America right now. The police are trained to lie about anything and everything and see no problem with this so long as their lies lead to an arrest. They don’t care that you’re innocent. That’s for the Courts to decide. They just want to make an arrest.
Know your rights. The ACLU has an amazing website which goes over your rights when being stopped by the police (or pulled over, or if they’re at your door). I recommend every American read this and become familiar with it!
Know your rights when filming the Police. You have the right to film the police when they are performing their duties in a public setting. You do not have the right to interfere with their “investigation” so if you’re going to film, stand back and use that zoom feature on your camera. Don’t argue with them, and don’t approach them.
The Police will lie. This bears repeating. They are trained to lie. They will lie and tell you that you have no rights. They may even threaten (or actually) arrest you. If you are arrested, say nothing.