Here are some tips I share in Nourished: A Memoir of Cooking and the Arts
1. For the microwave approach, lay out several sheets of paper towels. You can use two layers to make it easier to transport, or use a dinner plate. Separate the leaves from any woody stems. (Save the stems and bundle several together and use later on in soups or other dishes.) Remove any dirt particles on the leaves, toss leaves which have bruises or brown spot. Make sure the foliage is dry. Give the leaves ample room on the paper towel without touching each other.
2. Times for drying differ depending on the size of the herb foliage, the volts of the microwave, and the amount of leaves or plant parts being dried. Overall, times vary from 20 seconds to 3 minutes, usually no longer. Begin low, and check in increments of 20 seconds. After 30 seconds or a minute, touch one leaf and if it crinkles easily, then your batch is ready. If the leaf still bends, return it to the microwave for 20 seconds, checking periodically.
3. Once the leaves are “cooked”, carefully remove the paper towels to a flat surface. Fold the paper towel in half and half again, then press your hands on top of the paper towel, and flatten the area. You can use a small hammer too, or a meat mallet. Don’t be too heavy with the mallet, unless you want very powdery herbs. Shake the paper towel a bit after one time, and repeat the process. Store the herbs in a container with a tight lid.