It's important to keep your Christmas cactus well-watered, but make sure it doesn't sit in too much water. The best way to water it is to pour a small amount of water on the soil until it is moist, then let it dry out completely before watering again. If the soil is too wet, the roots can rot and the plant will suffer. Fertilize your Christmas cactus with a balanced fertilizer every couple of months, but don't overdo it.