The best way to start off is to practice with some one wall dioramas.  A one wall diorama is just a mini scene that you use to show off some particular object, outfit or doll.  They are fun and fast and give you a background to shoot against that can be easily set up and torn down in minutes.

To do these I usually just use a piece of colored matte board or a piece of foam core with wallpaper glued to it.  You don't even have to get that fussy.  All you have to do is use a cardboard box with wallpaper, fabric or scrapbooking paper attached with double sided tape.  Even wrapping paper or contact paper with a Barbie size pattern will do in a pinch.  (Just be careful with cardboard that if you attach paper that the corrugation doesn't show through.)

The picture below was done to show my bookcase when I first completed it.  All I wanted to show was the bookcase, but when I took a picture of it alone, I realized I needed something to put it in perspective and make it look real, so I added the chair, rug, lamp, pillar, bust and map to make it look like a library.  There are no side walls or ceiling and the single wall is just a piece of beige picture matting propped up against a box. This  took about 5 minute to throw together.  The floor is my kitchen table.

What you are looking for here is just a few details to fill in the gaps of what you want to say about the room, scene, person or object you are building the diorama around.

Here is another five minute diorama using the same background and my kitchen table top for flooring.  This was done only to show the bedding which I had received from the Doll Divas Christmas Diorama Swap.  (Thanks Barbara!)  The bedding looked rather masculine to me, though very cozy. When I photographed it I added a male doll, a dark trunk, a marble night table, and an oil painting to suggest a man's bedroom, and stuck to what might be considered more masculine colors.

Here is another that I used in my blog about the Morphing Mantle.  What you are seeing behind the doll is the bottom of a picture frame.  If I had been shooting it as a room, I would have put a piece of matte board behind it.  I was going to try for a few more pics and possibly add a backdrop, but my camera battery gave out and I had to recharge it, so I used what i had.
As you can see, it is a very simple scene relying on coordinated colors to give a sense of richness.  The outfit on the doll, the art vase on the interesting stand, the oriental rug and the rich fabrics used for the pillow on the sofa, give this room a rather upscale appearance.

These scenes can be as simple or as complex as you choose.  Try a few with whatever you have at hand, then move on to try some 2 and 3 wall dioramas.