The interior design is modular and you can easily work on either the Motherboard or the Opticals or the HD without disturbing any of the other components.

However, we feel that the most natural approach is probably to start by mounting the Motherboard, CPU, RAM etc. on the Motherboard assembly, attaching all its ancillary cables, and then slide the entire Assembly into the case. Next install the opticals and/or Floppy as they still use chunky old ribbon cables, so it helps if you have the maximum amount of room available. Finally install the HDs, and connect up their cables.