If you are using peel from lemons you plan to juice, remove the peel first. Never try to dry squeezed peel halves. They’re almost guaranteed to mold.
Once you have the peel, you can either spread it out in a single layer on an absorbent surface or a screen, or you can use heat. You can spread the peel out on a baking sheet and put in a 200 degree oven, or you can carefully microwave in 20 second intervals, stirring between each time, and watching for signs that it is about to scorch (which can happen quickly).