Haven't played in a bit. I've got what appear to be uncommon inefficiencies about using steel instead of candy (don't think I've ever really used candy for anything - just don't run my forts that long due to lag) and not setting up a military for a long while. I also don't tend to use marksdwarves often.
I have no idea of the efficiency of my layout. I tend to create a square main fortress with walls separating out nine internal blocks. On main levels, they all access the center block; stockpiles related to the workshops are located above and below. This is repeated entirely with a forge level, except the layer immediately below the forges is for magma - stairs extend through that (with suitable buffers of course) for storage of ores and bars. I dig all this out before letting in magma, as well as clear and smooth the layer that's going to be full of magma.
The nine main blocks also lend their shape to the walls that will follow the fort's perimeter on the surface. Sometimes I'll build a tower in the middle and build a roof over the rest. Sometimes I'll just channel out three of those blocks to create a surface farm. I can mess around with it a little.
Other than that, I create circular rooms (with pillars) on the edges for nearly anything else. Dining hall, barracks, trade depot, you name it. I usually wall up my initial entrance, creating a serpentine hallway that leads to my depot through my barracks. If I build traps, then the hallway branches into a much longer trap-free route for a wagon to use - a route which enemies will invariably skip.