To avoid confusion:
British English: basement, ground floor, first floor, second floor
American English: basement, first floor, second floor, third floor. The game uses AE.
Don't kill any CIA agents.
Disable security cameras (hacking a computer)
Download Data and bug the listening post (hacking a computer)
In general, while you're at it, search every room there is and collect everything there is and hack every computer there is. Pay attention to the 3rd floor, there is a room which is not connected, you need to walk around the atrium
What is in there:
Spoiler
There is gear to be collected, especially the best silencer "Mk3".
Bonus objective "use creative problem-solving" -- there is an air condition that can be manipulated (you'll see an icon hovering there, the same you see in front of TV screens) from inside one of the rooms on the second floor to get access to the room which doors are locked. There will always be one CIA guy on yellow alert after that, can't help it, that's normal.
Bonus objective "avoid detection completely": Don't even incapacitate them with tranquiliser rounds, shock traps or martial arts. Don't attack at all. Don't alert any other CIA guys -- except when escaping the listening post, the two guys at the exit will most certainly go on yellow alert while you open the door to escape. I use stealth armour suits and upgrades that avoid detection and, most effective, I use the invisibility skill of the stealth ability to sneak around unnoticed.
For some reason, even if you did everything right, the game does not show the last bonus objective in the debriefing. That is a bug, I reloaded from the beginning of the mission to make sure I did everything right and it went well, got 8/8 after that. So pay attention to the score, if it's 7/7 then something went wrong.