Let me begin by stating that this tutorial is oriented more at a beginner interested in interior design photography as opposed to a professional looking for advice on tilt shift lenses or portable lighting systems to further advance their craft. Obviously, some of these tips can probably be applied to a photographer of any caliber, so read away if I your curiousity has peaked.
I have been recently hired to take some pictures for an interior designers portfolio and thought that this was a good opportunity to document my experience and post a short tutorial on how I approached the assignement and post processing wizardry associated with it.
You are probably aware that you will need a wide angle lens. For big rooms you'll get away with something like 24mm on a full frame camera, but for tighter spaces I would suggest a Canon EF 17-40mm F/4L or the twice as expensive and faster Canon 16-35mm F/2.8L. Since you'll probably be shooting off of a tripod most of the time anyway, I'd go with the cheaper 17-40 and invest the remaining thousand bucks into a light setup or underpants. If you don't have one - get one. You'll thank me when you find out you can take really crazy portraits of your friends with their features distorted as if they just went through a birth canal.
During my shoot I relied heavily on existing light and compensated by sometimes taking multiple exposures of one scene if I felt one exposure was not going to cover it. I did learn that a good portable strobe setup would have been beneficial to further even out the illumination of the rooms. It's imperative that one does not abuse the strobes, however, since the lighting is an integral part of interior design and you don't want to overwhelm the natural light with your strobes. It's also important to mind the time constraints... jumping from room to room with a tripod is much quicker than moving your friggin umbrellas and setting up cords and looking for outlets.
One of the most important things to keep in mind are the verticals and horizontals when doing interior photography. You need to position your camera in such a way that the sensor plane / film plane is parallel to the walls. You don't want your wide angle to distort the view and @17mm the perspective will kick in at the slightest angle (what I mean by this is that if you tilt your camera upward or downward just the slightest bit - you'll see your vertical lines stop being so vertical, but rather converging at some point in the distance). Obviously there are exceptions to this rule. There's time when you want to exaggerate, distort, and break the sterile shapes and introduce an element of dynamics into the photos, but it should be done consciously, not accidentally.
Shooting really wide will also introduce some distortion to the pictures thanks to the properties of the lens you shoot with. With my 17-40mm I sometimes have to go back and adjust for barrel distortion with photoshop. There's a great filter under the distort menu - Lens Correction.
If you're shooting with a combination of natural light entering through windows and incandescent light inside, you'll have to juggle lights that are of two different temperatures. Manual white balance is usually a must, so shoot in RAW and adjust in post processing. I find it really helpfull to expose closer to the incandescent temperature, and then desaturate the blue channel to decrease the cool tones created by outside light.
Don't forget to shoot some wide shots and some detail shots of patterns, design elements, door knobs, fabrics, and so on. If you're running into really high contrast scenes - don't be afraid to use HDR images. I would advise against the super saturated unnatural looking images. More than likely your photos are going to be used for commercial pusposes, and HDR, if overdone, has a very amateurish look. Just like fisheye lenses, HDR should be used moderately and only when it adds to the easthetics of the image.