A squeezed lemon is awkward to grate. If you need both zest and juice, wash and dry the whole fruit, take the colored outer layer first, and cut it afterward.
Use a light hand so you avoid grating deeply into the white pith. Zest supplies aroma without much liquid, which makes it useful in a bean topping or a thick dressing that you do not want to thin.
You do not have to use the whole lemon at once. Store cut fruit appropriately and plan a nearby use for it, such as a dressing or soup finish. If freezing zest or juice, label the portions. A frozen yellow cube is less helpful when nobody remembers whether it contains lemon juice, stock, or something sweet.