Oh, hmmm.... I really need to do some screenies for that. Putting that into words might not be so easy to understand without the pics to follow along. I will try to get it done as soon as I finish the tropical bath. I can tell you this for now though:
The first thing I do after I get a new "room" file separate from the entire map is break it down into layers. I actually start with the wall or floor - go carefully around them with the selection tool while zoomed, and copy them to a new layer. Next I do the objects that I am going to work on. For example, to create a new bed, I copy the old bed to a new layer on top of the blank floor (a copy of the floor filled in with a solid color.) I create a "new bed" layer on top of the copy of the old bed and start drawing. When I come to something that needs to be placed above or below something else, like pillows, I create another layer for them so I can move them as I need to. I hope that makes sense. I'll try to be a little more detailed and put up some screens soon.