Christmas cacti are commonly propagated by cutting off a piece of the plant and planting it into soil. The cutting should be about 4-6 inches long and contain a few leaves and a small amount of stem. Make sure to use a potting mix that has good drainage and place the cutting in a bright location that doesn't get too much direct sunlight. Keep the soil moist but not saturated, and you should see new roots start to form in a few weeks.