Dehydrator or Oven Dry
(these methods work best for less dry herbs such as mint, basil, etc.)
With the dehydrator simply follow the instructions on your dehydrator, and leave it for 12-20 hours! For the oven drying method simply place the herb on a single layer on a baking sheet. Put the oven on the very lowest setting and leave them for 2-3 hours. You will know that they are done when you can easily crumble the plant in your fingers.
Image from Home in the Fingerlakes