Spend extra time making everything perfect, paying attention to even the smallest details.
Though you may not notice the details while walking through a house, as soon as you take a photo, you will notice the wrinkles in the pillows, the crooked lampshade, the out-of-place chair, the uneven bedspread, etc.
Check the camera is set as follows:
Shooting mode either Manual (M) or Aperture Priority (A or Av)
This will keep the aperture fixed so that the depth of field remains the same for all shots.
Use a tripod if at all possible.
Using a tripod has many benefits. For example, it keeps you from getting blurry photos when you take the long exposures needed indoors. It also forces you to put thought into framing the photo (you will quickly see things that are out of place and make sure that the image is the way you want it).
Keep your camera level and at, or just below, eye level.
If your camera is pointed slightly up or down, vertical lines will appear to be at odd angles in the photo.