Wine is alive and needs and air-tight bottle to survive. Bottles sealed with corks should be kept on their sides. This keeps the cork moist, preventing it from shrinking and letting air in.
Wines sealed with a screw cap or synthetic closure can be stored upright. There is very little agreement on how to best store sparkling wine, though some say it ages best stored upright.
The ideal way to store wine is:
Tip: Storing wine at a slightly warmer but consistent temperature is better than storing in a place that swings from very cold to very warm.