Very few people own a perfect cellar but a north facing garage, under the stairs or an unheated spare room are usually our best options.
Never leave good wines in an attic as one lady I know did. £12,000 of good port boiled to worthlessness. All investment wines should be kept in professional storage under bond, i.e. not technically in this country. This means no duty or vat charges which is very important now that most potential buyers are overseas anyway. Kitchens are another no-go area for wine unless you intend to drink them soon. I am not a fan of the wine storage cabinets.
Only keep wines you intend to drink at home and the things to avoid are fluctuating temperatures, sunlight, heat, freezing, damp, sunlight and vibrations. Over a very long time very dry conditions and even houselights can have an effect. For a few years most wines will withstand a bit of bad treatment but the longer you intend to hold them, the more care they will need. An unheated north facing integral garage will probably store wines without problems for twenty years.

Decanting.
A lot of people are confused about when and what to decant. Here are a few guidelines. Wine that has a sediment like vintage port will need to be decanted after the bottle has stood for a week or two, to remove clear liquid from the goo at the bottom. For a ten or twenty year old bottle it is worth decanting a good few hours before drinking but less for very old ports of fifty or more years. For these I decant and drink without pause.
Young wines benefit a lot from decanting as the harsh volatile vapours in a red wine will evaporate first and the taste will be more mellow. An hour breathing will see a vast improvement, longer for young and very tannic wines. Old wines will not benefit from decanting so much or at all. If I am opening a Bordeaux over twenty years old I tend to just pull the cork and let it breathe for half an hour but a forty year old claret I will decork and decant directly into the waiting glasses. I have known these wines to go from delightful to horrid in thirty minutes.
Even white wines can often benefit by either decanting or breathing before they meet your lips.