Your wine 'cellar' might be an underground cellar filled with expensive rarities, to a few bottles kept on a rack in the kitchen. In either case, there are certain requirements for maintaining wine in good condition that you should know. In modern, well heated houses, some of these conditions are hard to find, though this is only really a problem if you have wines you intend to keep for the mid to long term - say 3 to 10 years or more.
The wines below (left) are shown lying in an underground cellar at a cool 10 - 12°Celsius, having no wild fluctuations in temperature, are dark and are free from vibrations; in addition, it is relatively humid. These are the ideal conditions for cellaring wines long term; modern homes can be rather unfriendly places in which to cellar wine.
The bottles are placed horizontally, this is vital for all wines with a cork closure that are being stored for more than a month or two. This means that the cork is kept in contact with the wine, preventing it from drying out. If they are stored upright (which you can and should do with screw-caps), the cork will eventually shrink, allowing air to enter and spoil the wine.
Constant temperature is far more important than absolute coolness. Ideally, an unheated cupboard where the central heating will not be constantly raising and lowering the temperature. Ideally keep the temperature down below 17°C, at home preferrably 13 - 15°C. Garages and sheds are not a good idea, as they freeze in winter and over-heat in summer. Dark conditions will avoid the wine's colour being spoiled, again a cupboard might be a good choice, but in any event try to ensure the wine is not in direct sunlight. Freedom from vibration is important. Constant agitation doesn't give the wine time to mature slowly. Don't site your wine rack next to the washing machine or spin-dryer!
Strong smells can taint the wine over long periods of storage - another reason why the kitchen or garage might not be the ideal site. Finally - keep a journal of all your wines, so you know what you have and when best to enjoy them. Do all that you can to keep your wine-log up-to-date, as the last thing you wish is to find a wine in years to come that is well past its best. Not only a lose of money, but missing an opportunity to share a special occasion with good food and friends.