It's situational.

Stop signs:

• School zones, I stop and track stand briefly, even if there's no other traffic. Just a good habit for when the school year rolls around.
• During school hours I stop and put a foot down, especially if there are parents around. Parent drivers at school drop off and pickup are the worst drivers. And I want to show the crossing guards that cyclists aren't the problem.

Other stop signs:

• If there's no other traffic in sight, I slow and roll through.
• If a vehicle is approaching from directly ahead or to either side, and we will both/all arrive at the intersection at approximately the same time, I stop, set a foot down and make eye contact with drivers before proceeding. Too often they'll wave me ahead, then change their minds and rush into the intersection. So I'll put both feet down and wait until they go. If they hesitate I'll fiddle with my helmet, water bottle, etc., to make it clear I'm not moving until they do.
• If I arrive at the intersection clearly before the other drivers, I stop and track stand briefly, then roll.
• If the only other vehicle is directly behind me, I slow and roll through. Most of the times I've been struck on a bicycle or motorcycle were from behind at stop signs. They always say the same thing: "Oh, I'm sorry, I didn't see you!"
  
  Same thing again Sunday when a driver rolled through, barely missing me. She was very apologetic, between glances at her phone. But this was a problem long before ordinary cell phones, let alone smart phones. We're just invisible to some drivers.
  
  If the vehicle behind me doesn't slow down, I don't slow down either and just roll through. And I have on video instances of inattentive drivers blowing through stop signs as we both arrived, barely missing me. I don't need another reminder that this is has personally been the most dangerous scenario for me.

Traffic lights:
Usually I stop at red lights and wait like everyone else.
Based on experience with a particular intersection I might clear enough room in a right-turn-optional lane to wave drivers ahead if they're stacked up behind me. Depends on the intersection, lane width and neighborhood. Every neighborhood has a different personality and drivers behave or misbehave accordingly.

The only exceptions are bad neighborhoods, dangerous intersections and dead red lights.

On dead red in a safe area I'll wait for two complete signal cycles. If I still don't get a green I'll roll at the next safe opportunity. The main exit from one end of the MUP to the nearest public street is plagued with a dead red. Not sure why it's never been adjusted since so many cyclists use it.

In some areas traffic lights are adjacent to underpasses with transients, druggies and aggressive panhandlers and too many blind spots and hidey holes. I slow and roll ASAP.

In a few areas I'll detour around a signal, taking a well lighted parking lot to avoid a known trouble area -- a traffic light immediately adjacent to a liquor store or convenience store where troublemakers hang out. Those intersections are often littered with broken glass too.

Technically it's usually illegal to avoid signals by cutting through parking lots but I know the cops familiar with these areas would understand why cycles and pedestrians do so.

In decades of commuting and riding city streets following these basic situational practices I've been warned exactly once, by a San Diego cop in the 1970s. One particular light near the airport would never change for cyclists. My commute was before dawn, well before any vehicle traffic, so slowing and rolling never posed any hazard. Most police ignore stuff like this, but some don't.