The Holiday Cactus (Schlumbergera truncata) is called a leaf cactus but is not a true cactus.  It is an epiphyte, those plants which live on other plants.
 
The Thanksgiving Cactus does best in medium indirect light. Prior to blooming in the fall, move it to a brighter location, but avoid direct sun. A spot that gets bright, indirect light is perfect. The soil should be kept consistently moist and should not be allowed to fully dry out. At the same time, a Thanksgiving cactus should never be waterlogged as it is sensitive to overwatering. Allow the top 1-2 inches of soil to dry out between watering