De-clutter
Clean out closets and cupboards. They need to be at least half empty.

Put away all "knick-knacks".

Arrange furniture to make rooms look larger and more open. Make sure people can walk around the room.

You may need to rent a storage unit and take some out, it is worth it in most cases.

Get rid of clutter in ALL areas of home, this includes attic, garage and basement.

Curb Appeal
Keep lawn mowed, may need to lay sod in some areas.

Bushes and trees need to be trimmed.

Plant some flowers.

Pressure wash home, drives, walks, decks...

Touch up or re-paint home and mailbox. Make sure color is neutral and fits with neighborhood.

Clean outdoor furniture
Make sure front door and area surrounding looks as good as possible. While the agent is unlocking the home the potential buyer will be standing there for awhile.

Make a great first impression!

Neutralize
Paint inside of home a neutral color that will appeal to most people.

Take down family pictures, you want potential buyers picturing their family in the home, not yours.

Clean
Always keep home "show" ready

Make sure that the kitchen and bathrooms especially "sparkle". Limit items on countertops too.

Put out fresh flowers.

Use air freshners.

Get carpet cleaned (replace if really bad or have pets or smokers).

Shine up interior fixtures (door knobs, faucets…)

Clean windows and window treatments. Make sure windows open easily. Make sure screens are not torn.

If you have a cat, empty the litter box daily. If you have a dog, clean their dog beds... often. If you have a pool, clean it often.