One of the keys to a good cup of coffee is the beans. I won't go into what beans are best as that is an treatise in itself, but buy the best beans you can afford. And by them as whole beans, not ground.

Store your beans in an air-tight plastic container. Metal containers can impart a metallic taste to the coffee. Exposure to air can cause coffee to oxidize, resulting in a bitter taste. Do not store your beans in the refrigerator, store them at room temperature.

Once you are ready to make coffee, that's the time to grind your beans. So get yourself a coffee bean grinder, and only grind what you are going to use.

Also important to a good cup of coffee is a clean coffee maker. Clean your maker often (most coffee houses clean their completely every night). Use vinegar to get rid of all coffee residue. If you don't do this, the coffee you make will come in contact with the dried, oxidized, bitter coffee residue on your maker, and it will pick up bitterness from it.