First check the exterior. If the outside, or "curb appeal" looks good, people will more than likely want to see what's on the inside. Keep the lawn and landscape nicely manicured. Trim the bushes and season permitting, plant some flowers. Be sure your front door area has a "Welcome" feeling. Be sure to put a fresh coat of paint on the front door if it needs it.
Pay special attention to the kitchen and bathrooms. They should look as fresh and bright as possible. They must be clean and odor free. No leaky faucets and a fresh coat of paint if necessary.
You want your home to look as spacious as possible, remove any excess or large furniture. Make sure that table tops, dressers and closets are free of clutter. Don't use your garage, to store these extra things. These areas also need to have the impression of space. Instead, put them into storage.
Make sure walls and doors, cracked windows, holes in the wall or stained ceilings are taken care of.