Shooting interiors:

• Get the widest lens you have and put it on your camera, it probably won’t come off until you’re done. 18mm is ok, but 12mm is better.
• If it’s a big job, maybe rent a wide if you don’t have one. It shouldn’t cost more than $30 or so for a day. Doesn’t have to be “pro”, just 12mm.
• Use a tripod, and your camera’s self timer, because shutter speeds will be in the 1 second range.
• Better, use a remote. My remote that works with my Nikon D70 and D80 was $16.
• Turn on  all lights in the room, and close blinds. Turn fire places on.
• Use your lowest ISO.
• Shoot into corners — 45 degrees — or straight on — 90 degrees.
• Shoot verts and horizontals, or whatever the client wants (ask).
• Adjust your tripod so that the camera is about 4-5 feet off the floor and ensure your lens is pointing level, not up or down. If you don’t do this you’ll get the dreaded “fun house” effect.
• If you don’t have software (usually Photoshop) to put together multiple exposures, don’t worry about them, but DO shoot both on, under-, and over-exposed frames. See http://www.dpreview.com/learn/?/key=auto+bracketing
• Practice at home.
• If you spend 5 hours shooting you’ll probably spend 5 hours sorting, correcting and choosing shots, so charge accordingly and let the client know there’s time involved in “post processing”.