Here's an actual experience of how NOT to do it.
Setting: 2AM Weekday, Parking Lot, 2 Cars parked. Just as one of the cars starts to leave from meeting with the car I was in, a cop pulls up in the lot. He does not attempt to pull anyone over.
The driver of my car opens his window to ask the police officer for DIRECTIONS TO HIS HOUSE (Big mistake #1).
The cop comes out of his car, and gets ID (There was probably the smell of bud lingering on our clothing at the time, don't know if he could smell it)
He asks what we are doing, and the driver says he stopped for directions.
Cop answers: Cmon, that's not what you were doing.
(Goes back into car and comes back)
Points at me: Hey, you're the one starting trouble over here weren't you? Do you recognize me?
I state that I have never been in this area before and that's why we were looking for directions (It's True).
He asks me if there is anything in the car that he isn't supposed to see.
I respond simply: No there isn't.
He asks me to step out of the car.
He does a surface check and feels something in the pocket. I pull out some money. As he turns to check car, I attempt to put "contraband" from pocket to belt, but I don't have enough time. He comes around again and pats me. He feels it in the pocket. He asks me what it is. I don't respond because I know I'm fucked. From now on, being quiet is the best thing I can do. He searches the rest of the car.
I face some very serious charges due to the underlying circumstances. I won't get into it.
The worst part, is that the driver later blames me for allowing him to search. I didn't allow him to search the car. I stated that I didn't have anything. His pat down was completely legal. He found contraband, and he had the right to search the rest of the car.
Biggest mistake? Driver rolls down the window to talk to cop EVEN when he isn't pulled over.
Moral of story? Drive your own car.