To take a cutting from a Christmas cactus, you'll need to cut off a piece of the plant with a clean, sharp knife or scissors. Make sure to cut the stem just above a node, which is the bump where the leaves are attached. Make sure to cut at a 45-degree angle for best results. Once you have the cutting, you can plant it in a pot with good drainage and keep it in a warm, bright spot. It should start to root within a few weeks.