There are several factors that contribute to a good cup of tea, but this can be a moot point if you haven't gone to the trouble of storing your tea properly. Tea is a somewhat delicate product. There are many varieties that don't age well and a few that do, but any one will produce a better cup if you keep in mind a few basic rules for storage.
There are essentially five main environmental factors that can contribute to the ruin of an improperly stored tea. Among these are air, light, heat and humidity. Perhaps it's oversimplifying a bit, but these potential pitfalls can be addressed by storing your tea in a sealed container in a cool, dark, dry place.
Of course, how you store your own tea at home is irrelevant if the tea has not been properly stored before you purchase it. While buyers can't have much insight into storage methods from the time the tea was harvested, you should be wary of loose leaf tea stored in glass containers on store shelves, as is sometimes the case.
Odor is another enemy of tea, something to keep in mind if you're storing tea in proximity to aromatic foods or spices. The type of container used to store tea may also have a bearing on the matter, as related in this in-depth article from the Cha Dao blog. Because puerh tea can be aged for as long as several decades, storage is obviously a very important factor with this variety. For some pointers on puerh storage, look here, here, here and here. tins, containers
For more general purpose tips on storing tea, refer to this article. Tea storage is a topic that comes up from time to time at various online tea communities, including here, here and here.
The decorative and aesthetic aspects of tea containers are beyond the scope of this article, but some have actually made it into major museum collections, as noted here and here. For more on tea caddies, refer to this history and this Wikipedia entry.