The best way I've found is to finely chop the herbs or crush them using a mortar & pestle. Then I add some sea salt and mix the herbs with some softened butter. I put the mixture in silicone cupcake moulds, freeze until solid then empty the silicon moulds into one large zip-loc bag. I just take a cube out each time I need it and melt into the dish I'm making.
You can also preserve fresh herbs in a jar full of salt, alternating layers of salt and herbs. There's a great
video on youtube if you look it up.