(1) Cops are never your friends, no matter how friendly they act. Ever. Ever, ever, ever! This is important to remember!

(2) Don't tell them anything they don't ask about. (Cop pulls you over and before he speaks you say, "Sorry I didn't indicate when I turned" - bang, you just got yourself a driving ticket for not indicating, even though the cop didn't notice). Learn to shut your mouth and only speak when spoken to.

(3) Similar to (2), if they ask "Do you know what you did wrong?" the answer is always "No". The cop has to be the one to tell you and the one to lay the charge. Never dob yourself in, even if you are guilty. It's their job to charge you, not yours!

(4) Despite all the above, don't be a dick with your answers. If you can answer something they ask (without volunteering something they didn't ask about), then answer politely and you'll be on your way (if no law was broken). Don't play the "I know my rights game" or refuse to answer just because you can - sure, you can, but you'll spend the next 3 hours arguing with them about it at a police station instead of just leaving after 5 minutes if you had just answered with a polite "Yes, sir, my bad, it won't happen again".

(5) If you do get taken to a police station or are charged/arrested, then all bets are immediately off - now is the time you do literally shut your mouth and speak only to say "I need a lawyer present before I say anything". By law, they cannot refuse this request and cannot demand that you speak without one. You can literally repeat that request over and over, no matter how frustrated they get. Remember rule (1).