This is a great tutorial showing all the steps to canning greens. In this case it is mustard greens but they can mostly the same. I like a mixture of greens because you get a more complex taste with the peppery flavor of the mustard greens along with the sweeter taste of kale and chard.
You could also can or add to the mix, beet greens, turnip and collard greens. You can also put up spinach this way but I don’t care for the texture and prefer spinach raw in salad over canned. It develops a kind of slimy feel when you can it. Greens are really easy to grow and some like kale will keep growing late into fall and get even sweeter after a frost. To use the greens come winter I like to drain a jar of them. Heat an iron skillet and fry a couple of strips bacon. Once crisp lay it to the side and add some sliced onion and chopped garlic to the skillet. If you like a little spice in your life you can also chop up 2 or 3 jalapenos and add to the skillet.
Saute the veggies until tender. Break the bacon up and add back to the skillet and then add the drained greens. Cook until heated all the way through and they are ready to serve. You can serve as a side dish or bake some cornbread to go with the greens and have the greens and corn bread as a meal. This tutorial for pressure canning greens is from Hickery Holler Farm and is very well done with plenty of pictures to show each step of the process.