There is almost a sense of authority that needs to be stamped right at the beginning, as long a you approach them on an equal footing, showing respect but no sense of sub-serveant (sp) behaviour there is seldom any bad feelings.
What happened to me recently has to go down as a classic tale....after being stopped by the police a young woman officer comes to the window and greets me. In an attempt to make conversation I politely say....."nice day" to which she replies.....
"thats easy for you to say, I am black I absorb the heat"