Deborah asked for ideas about preparing collard and mustard greens.
Steamed greens
Make the leaves into a stack, and partly roll them up. Using a sharp knife with at least a 5" blade, on a chopping board, shred the stack into slices 1/4" (1cm) across, and then chop that into 2" (10cm) lengths, more or less. Pack the result into a bowl (I use a 40 fl oz (1 litre) Pyrex jug with a handle), put in the microwave oven with a plate on top, heat on full power for 5 minutes. The volume will reduce by about half.
Dress as you would a salad - balsamic vinegar and olive oil, maybe with a teaspoon of flax oil too.
These greens need not actually be cooked at all, but they have a strong flavor, which is an acquired taste. Not something to serve to guests unless you already know that they like slightly bitter intensely flavored greens. Cooking them both softens the texture and lessens the intensity of the flavor.