You're aging the un-ageable
Such a rookie move. So you want to become a real, bona fide beer geek, yeah? First things first: you have to stock your brand-new cellar with some top-tier, enviable beer, the kind of stuff that sends your fellow forum ranters into drooling fits of jealousy. That's an excellent move -- as long as you're treating it right. Aging beer meant to be drunk fresh is a big no-no in the craft beer world, as each style reacts pretty differently to the effects of time. A number of maltier, heartier beers, like boozy barleywines, imperial stouts, Belgian strongs, most barrel-aged brews, and some sours and Scotch ales, can grow richer and more complex, something many beer drinkers really appreciate. The rest -- light lagers, kettle sours, hefeweizens, and anything hop-forward like pales, IPAs, and imperial IPAs -- tend to degrade over time and should never be stashed away.
You're exposing it to sunlight
This is also a big one. Hops, like a lot of plant-based materials, love sunshine on the vine but aren't so big on it once they’re cut loose. Hops contain isohumulones, light-sensitive little buggers that, at the first hint of sunshine, break down and begin to release some of the same unappetizing chemicals produced by, you guessed it, skunks. For this reason, light-hued or clear glass bottles are always, always a bad idea (though, curiously enough, citrus tends to neutralize those skunky flavors…). Instead, make sure you're sipping your hop-bomb from a brown bottle or, even better, a good old can. And if you're planning to do your drinking outdoors, make sure to drop your reserves in a shady spot.