The most important factor to look for is the quality of the skin. It should be firm and taught. Wrinkled skin on ginger means it's probably dried out and old. The skin should be easy enough to peel with your thumbnail. The ginger you're picking out should also be a bit firm to the touch as any soft spots indicate poor quality or that it's been sitting around too long.

Given that ginger is mostly used for its aromatic qualities, you should probably make your olfactory glands and fresh ginger best friends. Take that piece of ginger and give it a big ol' whiff. If it smells spicy and ginger-y, you've got a banging piece of ginger on your hands. You've probably noticed that most recipes barely use any ginger, it's a little-goes-a-long-way kind of spice.