Part of my New Year's resolution is to not buy crappy parmesan cheese. You know the stuff I'm talking about. It comes in a green cylinder with a snap lid. It's powdery, gritty, and utterly tasteless. Yes, there are better options than this crap, but what you REALLY want to get is the good stuff: PARMIGIANO-REGGIANO. Look for the rind stamped with dotted block letters or even a stamp. Examples here.
The quickest way to ruin a good chunk of heavenly parmesan is to not store it properly. The air in your refrigerator will carry the scents of other foods and get into food that isn't well protected. The best example of this is stinky ice. So gross!
Learn to properly store your cheese when you keep reading.
To properly store your cheesy goodness, remove it from whatever packaging it came in, be it shrink wrap or plastic bag. Wrap it in parchment paper, and then wrap it in plastic or zip it up in a plastic zip-top bag. The paper creates a barrier between the cheese and the plastic. It will also help to absorb any moisture that may get in and can cause mold growth. That's it. Easy!