Wine, like all food products, has a shelf life. Some bottles can keep for a decade or more in the cellar, others are meant to be consumed within a year or two of release. But the question of "longevity" shifts on its axis once the cork is popped.
With the exception of some massively constructed big reds (ex: Barolo) that need decanting and a few hours to breathe, prolonged exposure to air is not a good thing. Wine oxidizes. It browns and turns hard and bitter. And this process is temperature dependent.
The warmer the temperature, the faster a wine oxidizes. The more air in the bottle (i.e., the lower the level of the wine), the faster a wine oxidizes.
So the first order of business is to eliminate the air. Products like Vacuvin employ a rubber cork and a vacuum pump to manually remove the oxygen from the bottle. Other products like Private Preserve displace the oxygen with nitrogen. (The nitrogen gas is sprayed into the bottle, and being heavier than air, rests atop the wine as an invisible protective blanket.) A third product, Wine Shield, is a plastic disc that is inserted into the bottle. It floats atop the wine as a clear but visible blanket and likewise protects the wine from oxidation. (The disc is recycled along with the bottle.)
All three products work, but all three will work more effectively if you keep the wine cool.
Put your opened wine in the refrigerator. Yes, even the reds. By eliminating most of the air and slowing down the oxidation process by lowering the temperature, the wine will stay fresher longer.
In the case of the reds, just pull the wine from the refrigerator 20 minutes prior to drinking. They will come to temperature with a nice, refreshing edge to them.
But wine preservation brings up another issue, especially in the summertime. Although the old caveat says to serve red wine at room temperature, this rule was written before the days of central heating when the feudal lords lived in drafty stone castles with thick cool walls. Room temperature is too warm to serve red wine these days.
Light-bodied reds should be served between 55-65 degrees and fuller bodied reds between 62-68 degrees. In other words, cool cellar temperature. The kitchen is no place for a wine rack.
Red wine served at ambient room temperature in the summertime will taste of its alcohol…brandied and hot. If you don't have a cellar, place your red wines in the refrigerator for 20 minutes before serving. This will not chill the wine, but rather pull off the heat and put the alcohol and acid back in balance for a more enjoyable glass of wine.
Actually chilling a low-tannin red, however, can be a refreshing option when the mercury climbs. Lighter styled Pinot Noirs, Beaujolais, Valpolicella and Montepulciano can all take the polar plunge with relative impunity. But don't allow them to chill to the extreme.
Temperature abuse is not a good thing at either end of the thermometer.