What's a good strategy for designing a room with multiple objects in it? I'm getting into blender and am at the point now where I can model simple objects and do some rigging without too much trouble.  Now I'm trying to figure out the best strategy to model an entire apartment, but am finding it much more difficult than just modeling a single object.

First of all, the walls and ceiling are making it very difficult for me to look into my apartment.  I can hide them, but it's hard arranging the furniture with them missing.

What's the best way to create the furniture?  I'm modeling the couch, chairs, potted plants and similar things in the same file so far, but having so many overlapping objects makes the editing difficult.  Should I put these in separate files and reference them in?  Should I move them to separate layers?

Any good general tips for modeling rooms?
Room modeling tips



Transparent objects

It's often handy to make some objects such as the walls transparent for the viewport. For render they're still fully visible of course:





Furniture creation

It's good to keep the pivots of the furniture in the bottom, so that you can snap them to different surfaces with Face Snapping. You can easily rotate them around their local axis with R+ZZ (or XX or YY depending on the case):





Managing lots of objects

Sometimes it's good to make some objects non-selectable, like the walls. Layer Manager is a great addon for managing objects if you have them on different layers. 

Alternatively, parenting them to an empty is an easy way to make them non-selectable. Use Ctrl+Left click to affect all the children of a parent in Outliner:





Rendering

Sometimes it's necessary to place the camera outside of the room and mark the front walls as invisible to camera. Hiding them is not encouraged, because the light that comes outside the room makes it look dull. The light needs to bounce from the insides of your front wall:


room.blend