In my experience, cops are mostly looking for one thing...
1) Am I dealing with a person who is shady/ disrespectful/ criminal/ drunk/ bad-parent/ wanted/ etc.
You look them in the eye. You OWN whatever it is you did wrong. You establish you know your rights but you're not shady. You request a camera and a supervisor if something is asked of you that you're not comfy with.
They're scanning with their eyes, just looking for a # of factors to stack up... philly blunts, clothing, shoes, haircuts, kids, items in car, keychain, radio... they're profiling the shit out of you from the second they walk up, playing detective.
"i'm coming home from work, picking up my kid, heading to gym" = productive member of society.
"I forgot my seatbelt, my mistake. I was speeding, crap, I totally didn't notice. Sorry" = You OWN your breaking the law.
"I'm not shady, I'm not hiding anything, but I'm not comfy with a search" = Call your boss, it's gonna be a long and fruitless day here.
You'll be fine with those things. However, if you are slightly buzzed, on your way to buy pot, rolling with a few shady people, blunted senseless, in the middle of road head, or carrying a suitcase of yayo in the trunk... I dunno what the answer is then lol...