Well when I do map, I normaly have a few ideas for cool architecture, so I will draw some rooms, then a floor plan and keep working with that and then when I map it its completely different ! When I draw the floor plan I try and imagine walking around in the map and shooting people, and I can sorta think, hey it would be cool if there was some cover here and stuff like that.
Immerse yourself
Also depending on the type of map, I will make each main room first, then connect them or add corridors. You can also quickly do a compile of just that room without having to close up any gaps, since you can just hide all the other rooms and compile only visable stuff.