"I want a lawyer" over and over until they shut up and you get a lawyer. I'm not sure how relevant this is in today's climate of police seemingly shooting first and asking questions later, but it's good advice to anyone who comes in contact with the police, without bullets.
I'm pretty sure it's ok though, to say "Good Morning" or something innocuous like that if you happen to see a policeman somewhere. Just no interviews!
and here's the piece I saw on Facebook lately that prompted this: a piece on Vice titled "A Law Professor Explains Why You Should Never Talk to Police."