Hi, I had real problems with a stealthy approach for my first KGB mission. The issue is that I couldn't see where the guards where on the first floor.
What I wanted to do was run up and crouch down behind the cover available, but they just seem to stand up and get spotted. Do agents not hide behind cover in this game?
You can always hide behind door entrances so that's something I try to use as much as possible. If there's a door between you and where you want to peek you're safe to open the door without being seen.
Always treat stairs as highly dangerous areas to sneak in as they give you the least information about potential enemies. I typically look for the best angle to survey important stairs when setting up spotter support units.
Another thing you can utilize is to get an agent with a heartbeat sensor. Another trick is if you're able to observe one side of a stair to just hang out for a couple of turns to see if any guards above/below you are patrolling. Of course this still won't warn you about stationary guards. If you have to take a gamble going up or down a stair try to do everything else you can on the map first if possible so you don't engage combat too early in case you're spotted.