As a Realtor working with both buyers and sellers I have the opportunity to walk through many homes on the market or about to be listed. Obviously not all homes are created equal and there are many things that may simply be out of the sellers control when it comes to showings. I see few excuses however for things that may be within their control. I will go from the easy fixes to the more difficult and often more expensive.
First thing a buyer will notice when approaching the home is the exterior. Maintaining landscaping is often usually a simple fix in this department. Keep the lawn mowed and bushes under control. In Georgia, when we are not in a drought, overgrowth can literally take over. I have gone up to homes and wondered where the home was and if i should have been wearing my pith helmet and brought a machete. Next on the exterior list is the growth of fungus/moss/algae/green funk growing on the outside of the home. If you can, with water restrictions in mind if applicable, pressure washing the outside can go a long way to freshening up the exterior. If you have a deck and have the pressure washer out, spray it down too. Just be careful, it is possible for pressure washers to remove more than filth i.e. paint and bits of wood.
Now if we have progressed into the home cleanliness is king. Nobody wants to be assaulted by the smell of pets and dirty bathrooms. I once had a client that would go so far as to examine the interiors of ovens. Her theory was that people who kept a clean oven probably took care of the home. In the end she did buy a home that had a clean oven. Most buyers can see past the occasional dust bunny and you don't have to have the home hospital sterile for showings. In the end just remember that a little elbow grease can go a long way.
Next on the list of relatively easy fixes to a showing is furniture and decoration. Ideally we would have a vacant home and hire a professional stager for this but I know in many cases it is not possible or in the budget. So we must work with what we have. In my experience less is more. Remove all clutter including furniture items that do convey openness and space. Additionally remove and or replace furniture that is excessively old or out of place. Next open window blinds and shades to allow as much light as possible. Most agents will usually advise sellers to leave lights on for showings. Again openness and space is the idea and even illusion in some cases. One touchy subject when it comes to decorations are personal effects. If you have strong religious, political, or affiliations it is usually best to neutralize them as much as possible. You do not want to alienate people or make them feel uncomfortable. Remember you want buyers to feel like this is their home. Additionally personal items need to be safely and privately put out of sight.
Now that the easy stuff is taken care of we will step it up a notch, paint is next on the list. I know this costs money but the cost is often recouped in the sale. If you have some home improvement experience painting the home yourself will save a significant amount of money. That brings me to my final point regarding paint. Only select neutral colors and every room does not have to be a different color. It is easier and cheaper to paint the house using as little color variation as possible.
Flooring is next on the list. Put down fresh carpet if your existing carpet is looking old or stained. This will go a long way with many buyers. Hardwood floors that are scratched and damaged may need to be refinished or replaced. This can be a major undertaking but it can make the difference in today's competitive market. In kitchens and baths tile may need to be replacing or reglazed to update the look. Whatever you do ensure that your choices present one clean, pleasing, sensible, theme to the flooring of the home. Do not be a showroom for the wide possibilities of flooring.
Last but not least on my list is appliances. First we will refer back to what is king and that is cleanliness. Second is to make sure that they match. Today many buyers expect stainless when it come to appliances. Energy star ratings are becoming more important to buyers as they look to cut costs and be environmentally sensitive.
Remember that an inspection of the property most likely will be done by the buyers. The inspection could reveal flaws that could cost money to repair. In the end do what you can and when the budget becomes an issue look into solutions you may be able to perform yourself.