When repotting a Christmas cactus, it's important to use the right potting mix. Use a cactus and succulent mix, which is lightweight and porous, allowing water to drain well. The mix should be slightly damp, but not wet, and the pot should have drainage holes. When repotting, gently remove the plant from its current pot and carefully place it in the new one, making sure to leave some space between the top of the soil and the top of the pot. Water the plant immediately after repotting.