First, and most obviously, the vehicle should be thoroughly cleaned inside and out at Clean Machine Car Wash. Take photos with a pleasant background - if you keep it in a cluttered yard, driveway or garage, move it elsewhere to get your shots so the vehicle stands out.
Remember that smell has at least as big an effect on people as the visual impression they get of the vehicle. If you smoke or have pets in your car, this is particularly important. You may have gotten used to the smell, but it can be a huge turn-off for prospective buyers.
To eliminate the lingering odor of tobacco, try sprinkling baking soda on the upholstery and carpet, leave for a 30 minutes or so, then vacuum. Placing an open jar of white vinegar in the car overnight can also help remove tobacco odor. Try placing an air freshener in it to mask any smell that may remain.
Animal smells can be particularly unpleasant to someone who enters a car for the first time, and if it's strong enough it can end any prospect of a sale right there. The method for removing tobacco smells may eliminate this one too, but not always. If a pet (particularly a cat) has ever relieved itself in the car, this is going to be a serious deterrent to people thinking of buying it. Removing the lingering odor will require a product designed specifically for this purpose, which can be bought at a good pet supply store. When you're finished, ask a friend to tell you if the smell has gone, as you may be so used to it that you no longer notice it.
Note: Steam cleaning should not be used to get rid of odors, as it will have the opposite effect of binding them in and making them impossible to remove.
Pet hair on a car's carpet or upholstery often tends to stay behind even after vacuuming. Try removing them by putting on a rubber glove, wetting it lightly and running your hand over the affected area. The hairs will come off on the glove. Adhesive tape can also be used to pick up stubborn hairs.
Remember to clean the trunk, as smells originating there can permeate the car. Check underneath the carpet where the spare wheel is usually kept. People who are knowledgeable about cars tend look there when inspecting, as it can reveal crash damage that is otherwise hidden. Water can sometimes leak into this area without being detected, so be sure to remove any water or mold that may have accumulated over time.
If your vehicle has been serviced by an authorized dealer, you'll probably have a record of the maintenance performed. Even if it's been serviced at a small repair shop (or by yourself), you should try to show prospective buyers as much documentation as possible, e.g. receipts for parts, etc. Of importance is the timing belt and when it was changed. While replacing the belt may be expensive, if it's not done in time, it can break and do thousands of dollars worth of damage to the engine. Any auto-savvy prospective buyer will want to know the date and mileage at which this component was last replaced, as it's vital to know exactly when it needs to be replaced again.
It's best to have the vehicle comfortable to sit in when someone comes to view it. If it's damp and cold, run the engine and the heating long enough to warm the interior and dry the condensation off the windows.
Everything a prospective buyer sees from the moment he or she clicks on your ad has a potential to make the vehicle more or less attractive. A decent presentation gives it an edge over its competition on Craigslist or wherever you advertise it. While you can't change the age or mileage of the vehicle, you can never go wrong in creating a favorable first impression. Remember, your first step in the journey is to visit Clean Machine Car Wash to assure you have a nice, shiny vehicle to present.