You’ve probably been at blender for a while raycat, judging by when you joined here - but anyway I’ll give you my workflow if it helps…
For heavy scenes I will render just certain layers - if it’s a room, I will just render the room with a single object in it, then as the lighting improves the way I want it, I will then move onto engabling other layers to test them. Then do the full render when all looks well. Reducing Subsurf for the render can speed up things drematically - might not look great, but if you’re just setting up the lights/shadow/mood, then who cares about the details. I guess it really depends on what your scene is though.
You can also try turning off Ray tracing and Shadows under the Shading rollout of the Render TAB. Disable anit-alias, render at half-size. Turn off those soft shadows you may have on your lights. Under Sampling just use 1.0 for sample and 1.0 for soft size. Set all reflection/mirror materials to use 1 ray bounce.