What I do is put the idea of the fic in the center circle and then draw a couple lines off in all directions.

Start general, naming the lines like "Characters" and "Events" and "Setting" and then let the lines branch off into finer and finer details until you run out of page. When you do, you start a new page with a new map with a finer focus, for instance, "Characters" can be its own map.

It really helped fill in the vacant spaces in my ideas. Helped me see the imbalances and where I needed more meat and details.