Pick up every room.  Straighten or remove newspapers, magazines, mail, toys, clothing, sports gear and dishes. Make the beds and plug in the deodorizers or other good smelling stuff and empty all trash cans (make sure empty cans are clean).

Open all blinds and shades. Turn on ALL lights whether it is day or night (closets and utility rooms too).

Maintain a comfortable temperature winter and summer.  You want the potential buyers to spend time in your home and not hurry through because it is to warm or too cold!

In winter make sure all sidewalks and steps are free of ice and snow (for safety as well as appearance).  In summer keep lawn mowed and sidewalks edged etc.  If you have automatic sprinklers, schedule them for early morning or late evening when there are few showings, that way potential buyers have the opportunity to walk around the exterior of the home and check out the yard without getting soaked.

Vacuum all carpets. Especially if you have pets! Sweep the kitchen floor, dust if needed.

Make sure there are no dirty dishes in the sink or crumbs on the counter.

Last but not least, take the cat, cat litter, and or dog out of the home before the showing. I know this is not easy.  I recently moved and had to drive around for hours with 2 very unhappy cats and 1 hyper dog.  It was not fun but it was necessary!  The cat litter should be removed if possible, but if not at least clean it immediately before you leave or put it in the garage.  If you have guinea pigs, hamsters or other small pets make sure the cages are cleaned daily.