Patch all holes and cracks in walls and ceilings. Check with your local Home Depot or Hardware store for the items needed to make these easy do it yourself repairs. Inspect every room for spider webs and lint clinging to ceilings. A simple long handled duster will make short work and give a cheap face lift to an aging room. Don't forget to dust the tops of light fixtures with fans- consider temporarily removing the blades and washing them.
Fix all broken appliances (or replace them with mid-range priced appliances). White appliances will appeal the most, with black or stainless steel coming in second. Mid-Range Appliances even cheaper appliances will dress up a kitchen more than costly but old, stained and highly used appliances. If you can't afford to purchase new appliances think about adding an appliance allowance of cash in your negotiations on final price.
Get the HVAC system checked out by a professional with detailed facts and estimates in writing and cost of repairs if any (a good bargaining tool in your pocket if they check out in good shape).
Repairing simple gasket replacements on leaky faucets and using a polish created for bathroom/kitchen plumbing fixtures will go a long way toward making a good bathroom impression. Anything that is a mirror surface is attractive to buyers if they can see the shine.
If your carpeting is badly stained and worn in places (be brutally honest when you evaluate the condition of your carpet) - replace it with cheap (to save costs) but clean carpeting. This is a trick that many people who buy homes cheap and sell higher (flipping) use. Keep in mind that the new buyer can replace the carpet in time if they desire, but carpeting is seen as a costly replacement at the negotiating table. Be pro-active and get it done first with a cheap carpet, perhaps thick padding and neutral color. Then take your shoes off each time you enter the house until the house is sold to keep that brand new look.
Remember the Addams Family Home on Television in the late 60's. Do you have broken, chipped or cracked windows that painfully remind the neighbors (and any buyers) of the Addams' home? Replace every broken, chipped or cracked window pane now. Then wash them so that sunlight streams through them. If you aren't able to reach them or have a physical injury/disability that prevents climbing on ladders ask someone to help you with this task, be it family, friends or hiring labor for a day to get it done. Some communities have charitable organizations that will help freshen up a home for elderly or disabled residents. Check it out.
What is happening under your roof? Most of us have no idea. For this reason have a professional inspect the roof and write you a detailed fact sheet on the condition of the roof. You can bet the first buyer and every buyer after that will inspect the roof visually first thing as this can be one of the most expensive repairs that any home has. If you know in advance the roof may be an issue you will have pro-actively established the amount you will allow in the negotiation of the final price.
Clean and repair all light fixtures so they shine. Then replace every bulb with a brighter one which provides the full spectrum of light. Colors will brighten. Bright is Right when selling a home.
Consider taking down even fairly new drapery which can hide odors and replacing the cloth window treatments with thin white vinyl slat blinds cheaply purchased at a discount store and easily installed with a few tools. White is always the right color for a buyer. To a buyer white is like a new canvas upon which the buyer can paint their own picture of home.
Hire a home inspector FIRST (most likely the biggest cost you will face but the one that will give you the most return on your money when the negotiating starts). If at all possible get a real estate agent to provide you with three different names of local licensed home inspectors used by banks. When the negotiating starts you will have fixed all of the minor issues with your home and have a price (estimates provided by the inspectors)