Excellent 45 minute ACLU documentary on how to interact with police in three situations: traffic stop, in your house, and on foot.
BUSTED: The Citizen's Guide to Surviving Police Encounters http://www.youtube.com/watch?v=yqMjMPlXzdA
tldr:
-say as little as possible.
-be courteous and don't argue or complain.
-memorize the phrase "I do not consent to any searches."
-do not invite police in your house.