Here's an overview of the map, including call-outs that are helpful to know.
Then you have the stairs between B-halls and mid. If they rotate from B to A they can simply drop down the stairs and be there in no time. It takes a lot longer to run up the stairs and rotate from A to B.
The lone soldier on A
Unless you notice that the terrorists have a tendency to attack A, I would recommend to play with only one defender on A. His job will be to support the B-players as much as he can as well as to push for information and call for backup if needed. A lot of the time he won't need his smoke, so he can throw it over to B and smoke off long. That way you'll have four smokes ready on B.
After that he should sit around corners at CT ramp, long A or stairs. He will listen for footsteps and check for flashes and smokes. If he thinks that they're coming to A, he should try to survive for as long as possible. If the B-players manage to take control over long B or other key areas around B, the A-guy can fall back to the bombsite and one of the players from B can rotate and support him.
If he can't see or hear anyone he can try to move in for the backstab through Z. If he does, timing is crucial. Wait for the terrorists to initiate their attack, or else there’s a good chance they will have at least one player waiting for the lurker coming in from behind.
Should problem arise over at B, your brave soldier from A shouldn’t hesitate. He can either go in through connector door and call for a flash from drop room or throw the flash himself. This flash will blind any terrorist tucked in the corner outside door, making it a lot easier to initiate the retake attempt.
On the next page: getting creative around B.
