Wrap in damp paper towel or plastic bag and refrigerate for up to 1 week.
Freeze: wash, de-stem, and blanch leaves for 2 minutes (dunk in boiling water for 2 minutes), rinse in cold water (ice bath) to stop cooling. Drain and freeze. I like to lay fruit and veggies out on cookie trays to freeze, then pack them into plastic bags after they are frozen.
Dehydrate: Assuming you don't have a dehydrator (if you do, follow those directions!), wash, trim off stems if desired, and pat dry. Place a single layer on a cookie sheet, pop them into your 200 degree oven for ~ 20 minutes. Keep your eye on them towards the end -- they can burn easily. They may need a little more time, so pay close attention. Once you have the timing figured out for your oven, write it down somewhere so it will be easier next time.
Crumble up those greens, and then add them to eggs, smoothies, soup, stews, sauces--whatever you can think of!