Know your right
Ignorance is not an excuse under the law. So, try as much as possible to know your right and privileges. It will really come handy when a policeman is attempting to be smart by referencing or quoting non-existent laws. If you are not a lawyer, you will definitely fall for this. Your car may be tolled or you may end up offering a tip to the policeman. At the very least, know the necessary documents to share with share with the police when flagged down.