I put a dash of olive oil in a skillet, cook the beets until they're slightly browned, add the greens (really well rinsed, and still pretty wet), a sprinkle of apple cider or balsamic vinegar, a T or so of tamari (wheat-free soy sauce), and sometimes some sesame oil and/or sesame seeds, put the lid on, turn down, and let cook until well wilted.
You ca nuse other seasonings, but vinegar is important on any dark leaf, as it cancels out any bitterness.