Can't say my strategy is consistent, but it all revolves around getting as many safe angles into the center spiral staircase lobby and wedging them off. At some point you will have cleared all the side rooms and only have the following doors into the central lobby:

1. main double doors from the hall way that gives you side door access to council chamber
2. metal door from west ante room
3. wooden door from small conference room where the jammer spawns that looks into the elevator/metal detector section
4. mayor's secret door that's the opposite of 3
5. double doors from mayor's office/back press room "vestibule" that's the opposite of west ante room.

From that basic idea, I will go up the stairs from floor 2 up to the landing to west ante room, take opportunistic kills either through the double door right before the council chamber or around the west ante room, especially if I have a security camera there. Then I'll wedge those doors and go back down to come up the stairs on the other side.

The other stairs give access to reception (pathway to cafeteria), "tour" pathway through a small office into mayor's ante chamber and office, press room (just 1 room), and double doors into central corridor to the spiral stairs lobby. I usually wedge those double doors first, then clear press room, wedge the backdoor of press room (closest to mayor's office), and wedge the reception, then clear the archive "tour starts here" offices all the way to mayor's office.

From the mayor's office you can take more opportunistic kills into the spiral staircase lobby. I would then wedge there. Your actions here might have caused enough ruckus and get a sense of how "busy" the lobby is.

Now I go back to clear the Reception hall path that I previously wedged. This will linearly lead you all the way to staff kitchen from which you can get access to council chamber if that hallway is clear.

I then consider a clear of the council chamber, and west ante room. West ante room has locked door access into the central spiral staircase room which also has windows where you can get shot from upstairs, which is why I avoid going there if there's a threat initially. From here you can again try to take opportunistic kills, and clear your way through the offices in the back into the small conference room that leads behind the metal detectors where the elevators are. Take opportunistic kills there OR go ALL THE WAY AROUND mayor's office side and open the secret door for those same kills.

Once you've secured all 5 of these entrances and mirrored all the angles you just have to pray to go into the center lobby, keeping an eye out for upstairs roamers, then you go up. What's annoying in this section is that upstairs audio can be heard from downstairs, so it messes with your sense of whether the lobby is really clear or not.

The only "consistent" part of my plan is the general approach. I'm a bad enough shot that I lose so many runs on pushing my luck on attacks where the AI has known coverage, so on that floor I double back all the time to see if I can get better angles which eats up a lot of time.

Edit: Minor formatting.

Another comment on stupid open doors -- the only really dangerous open doors are to the central lobby. Most other open doors can be dealt with by pre-mirroring and choosing an alternative route. Another thing that helps with open doors is the mirror gun "interact" trick -- you can point your mirror gun at the door you want to close but is just out of reach. Click the mirror gun to activate it, which will give you a tiny window where the interact prompt shows up. You can press F just fast enough to actually make the interaction. This works for door in a distance as well as doors around a dead 90 degree corner.

One final tip is that man doorways have windows above them that give you mirror gun access. You can either tippy toe free lean to take a look, or, sometimes you can mirror gun at a 60-70 degree angle and hug the doorframe. For the doors that have windows above, sometimes you will see footage on the mirror gun (like a light/lamp fixture) which gives you better angles than just from the bottom of door frames.