This year is the first that I have successfully preserved herbs from my garden. I took the leaves, whizzed them up in the food processor, put in some oil (I used a mix of expeller pressed coconut and olive) to coat, scrape it out into a ziploc bag. I froze it in a very thin layer, and when I need it, it is easy to break off just the size chunk I want. The flavors are preserved very well. I am really happy with the way it turned out!
In other years, I have dehydrated the leaves or put them in the freezer whole. Dehydrating the leaves takes away the flavor and makes them tough. Putting them whole in the freezer is better, but there can be that freezer flavor if they stay awhile. I am hoping the oil will keep out the freezer flavor.