To propagate a Christmas cactus, first, choose a healthy leaf that is about 6 inches long. Then, cut the leaf at a 45-degree angle, making sure to include the stem. Next, dip the cut end in rooting hormone and place it in a pot filled with well-draining soil. Keep the soil moist but not wet, and place it in a bright, indirect light. Finally, wait a few weeks until roots start to form before repotting the cutting.