A thorough cleaning is the single most inexpensive and important thing you can do. Scrub the fingerprints from your woodwork, disinfect and bleach any mildewed surface (be a zealot with bathrooms), clean the basement, box the miscellaneous, straighten all of the closets. Even the most woebegotten house around gets a major - we mean major - facelift from having the windows washed. Sparkling windows affect a fabulous change.

Remove the "junque" from the countertops. Put away all of those appliances which you use twice a year. Not enough storage? Buy some freestanding shelving and use the vertical space.
Remove any old, worn, stained or smoky carpets.

Replace dim, low wattage light bulbs with 75+ watt bulbs. After all, it's now cleaner; it might as well be brighter and therefore more cheerful. We've never had buyers say, "How 'bout showing us something dark and dreary?"
These things, folks, will cost you little or nothing and it means INSTANT equity.

Actually, most of our clients who do these simple things wonder why they didn't do them for themselves earlier. Maybe you won't want to move!