A twenty-four millimeter wide angle lens sees an angle of eighty-four degrees, sufficiently wide for our purposes. A wider angle lens starts to show too much distortion through foreshortening and a less wide lens will make the room seem smaller. A second choice of a twenty-eight millimeter lens with an angle of view of seventy-five degrees is acceptable. A trick I have used to increase the width of view is to shoot through a doorway, just missing the sides of the opening. Unless you own an expensive perspective correcting lens, a distance of four feet from the floor is ideal to prevent convergence (when the walls appear to tilt in). If you own a digital camera with a 28mm lens, perspective can be corrected digitally with software from Adobe Image Ready or the equivalent. Most wide angle lenses share the fault of barrel distortion. This can be corrected with software from radcor.com.
Walk around the room and choose a view that includes the best look for most of the furniture. Two different views may be necessary to tell the whole story. For a spacious look, shoot into a corner, slightly to the right or left of dead center. Pictures taken at right angles to a wall look constricted and less spacious. Interesting table tops will look better from a higher angle. Be sure to light all lamps in the rooom.
Another method of presenting a whole room in one picture is to use the stitch method. First find the center of the lens node. This is a point halfway between the front element and the sensor chip. Place the camera on a tripod, attached at the node point. Level the camera, set the lens on 50mm* (equivalent) and take several slightly overlapping pictures. The images may be stitched manually or helped with software for that purpose. Be sure to smooth any indications of joining.
While flash on the camera is safe and will render the whole scene in accurate color, too much is lost in the way of depth, highlight and shadow detail and in attaining an interesting look. Flash on the camera flattens the scene, reflects unnaturally off flat surfaces and introduces a dark shadow around every object in the room. A better lighting includes a single bright light in a large reflector and a second light bounced off the back wall not appearing in the picture. Items of a dark nature like a dark stained cabinets need an additional spotlight in order to balance the tones in the picture. Night time pictures avoid the problem of overly lit windows, but if the window treatment only looks good with light coming through the window, time your photos at dawn or at dusk. The bluish light entering the window at these times while not matching in color temperature is quite dramatic and attractive. This blue light can be corrected later in the computer.