Whenever I'm given (or purchase) a nice bottle of wine, I'm immediately faced with the question of whether or not it's something I plan on drinking right now, or something I want to drink later.
Most people aren't storing a ton of wine these days, but when you come across a bottle or two that you do want to save for a few years (or a few decades) it's important to make sure you're saving that wine the right way.
Keep Them Cool
The best thing you can do for your wine is to keep it at a cool, stable temperature. If your wine gets hot, it can end up with flat aromas and flavours. The ideal temperature to store wine is between 7-18°C degrees, and you never want it to go over 21°C. Your fridge isn't really the right place (unless you're storing that white wine you plan on drinking for dinner) because it gets too cold and might dry out the corks.
Instead, opt for a nice spot in your basement or the back of a closet that stays cool. Or, if you're storing a number of bottles, spring for a wine-specific fridge.
Light is an enemy of wine (and beer). Make sure where you choose to store your wine it stays dark and isn't getting exposed to direct sunlight.
Getting exposed to sunlight can make your wine prematurely age and degrade the overall quality of your wine. If you really want to play it safe, use incandescent bulbs whenever you're storing your wine over fluorescent ones, although both are probably fine.
I studied in France in university and brought a decent amount of French wine home with me. Some of that wine got consumed with friends pretty much immediately, but a few bottles I've held on to and moved from apartment to apartment over the years, saving them for a "special" occasion.
Store Them Sideways
There's a reason wine racks all store wine on their side. Storing your wine on its side keeps the wine touching the cork, which keeps that cork wet and prevents it from drying out. You don't need to store wine with screw caps or plastic corks on their side (but you can), but corked wines should absolutely always be stored sideways.
Keep Things Consistent
If you can, try and avoid moving your wine if you don't have to. There's some that argue that vibrations can impact the quality of your wine in the long term. While a few bumps every now and then probably aren't going to do much, it's best to limit the movement of those bottles as much as you can.
Know Your Wine
Don't just buy bottles and store them away. Talk to the wine producer when you buy and see what he or she suggests as far as how long to age a bottle. Some wines can be aged for 20 years or more and will only get better. Other wines need to be consumed within a few years or they'll start to change in a negative way. Know what you're storing and when it should be ideally consumed.