The best way to root a Christmas cactus is to start with a healthy cutting. Cut off a piece of the stem, making sure it has at least one node (the bump where the leaves meet the stem). Then, dip the cut end in rooting hormone powder and plant it in moist, well-drained potting soil. Make sure to keep the soil slightly moist, but not too wet, and to place it in a bright spot with indirect sunlight. Wait a few weeks and you should start to see new growth.