How to Store Fine Chocolate
The best place to store chocolate is in a cool, dry, dark place -- like a pantry in the basement. You want it cool enough not to soften the chocolate but not so cold (like in the refrigerator) that condensation will form when you take it out. Condensation dehydrates chocolate and downgrades the texture and flavor, and it can also cause "sugar bloom," the unsightly white or grayish spots caused when the sugar rises to the chocolate's surface.
Also, chocolate will absorb the smells and flavors of the foods stored with it, so although it doesn't normally have to be kept in an airtight container you might want to seal it up if you'll be keeping it in a pantry with something pungent, like onions.
As a general rule, fine chocolates (especially those with fillings) should be eaten within a few weeks to a month for the best flavor and texture. When stored properly, however, milk chocolate can last up to a year and dark, unsweetened chocolate slightly longer.
Note: If you must store chocolate in the refrigerator (i.e. you live in a very hot and humid climate) then keep it in an airtight container and let it come to room temperature before opening or unwrapping it (to help prevent condensation).