Great tip from Cole Ruth, published by Saveur:

Here’s a trick: zest a lemon and let the zest dry on a piece of wax paper for a day, then fold the wax paper and press. Presto! The zest becomes a powder. You can sprinkle some onto a beet salad to give it a zingy flavor or throw a pinch on a slice of Key lime pie for more tartness (you can make dried zest from limes, too, for that matter).