The police department is a vital branch of the executive arm of government, in accordance with the nature of the constitution.
But they have been known to be one of the most damned set of professionals, due to the their aggressive and barbaric manners when dealing with civilians. Those men in black uniform can make your life miserable in the twinkle of an eye if you don't apply some safety precautions.

In order to save your self the trouble of this cobwebs, you must put some things away and attach something.

Such as;
For instance, a set of policemen bursted you in your resident (the first thing, they feed on is your fear). It's fine to shocked, but never find to be afraid.

No matter what happens (try not to take to your heels) running away is not part if the plan. You might get shot down instantly and that's the result of your nervousness. Now they come closer, let's say you finally became their target, keep it cool.
Quickly read their moods (in order to know how to rapport) with them. They don't usually greet, you just greet them it cools off their aggression.

They'll ask for your identity( which you should not provide, apart from your names and nature of job, and probably your ID). Anything apart from this you have the right not to say.

As soon as they say "you are under arrest", boldly ask for their IDs and warrant of arrest.

Tell them you'll accept being arrested if those are provided.

Note, if they are unable to provide those, know that they are wolf in sheep's clothings. If they can forge an ID, they can never forge warrant of arrest. This way they are meant to back off.

But on the other hand, they provide those documents, ask for the grace to inform your lawyer when you get to station. And he'll handle it from where you stopped.