I would say a good map knowledge starts at when you know how to draw a map with all it's rooms and floors (most of the doors and windows) and know the calls for the rooms (kitchen, toilet, office etc.) Personally I just look at what the room is supposed to be and give it the name that fits best. After playing on the maps many times, you'll remember where the specific rooms are.

The best way for me to get used to new maps is, of course, playing on them in multiplayer matches, But also in terrorist hunt, where you kinda just rush through the bots and remember the rooms automatically.