Set blinds at one level or drapes drawn evenly. Keep the house tidy but with a relaxed atmosphere. Have the garage clean and tidy. Broken window panes or loose door knobs make an unfavourable impression. Fix the minor items - sticking doors, broken switches.
Buyers spot the small items then start looking for problems.
If you have a dog, keep it out of the house and under control. Many people are afraid of dogs. Keep the TV or radio off or turned down during inspection. They can distract people. Let plenty of light into the rooms.