At a minimum, the house should look clean and organized.
Decluttering counter tops of personal items go a long way in making a home look open and inviting.
Smaller things, such as removing visible garbage cans, can also make the house look cleaner.
Bright, artificially-colored packaging, like on cereal boxes and shampoo bottles are also very distracting to the eye.
Perhaps most important, check to ensure every light fixture in the home turns on with a working light bulb.