Holiday cactus (Schlumbergera) need cool temperatures and short day length to form flower buds. Thanksgiving cactus (S. truncata) normally blooms a bit sooner than Christmas cactus (S. x buckleyi). Care requirements for both plants are essentially the same. To induce bloom, give the plants a rest period in fall. Keep them on the dry side, but water enough to prevent the flat, leafy stems from shriveling. Maintain temperatures in the 50s to set the most flower buds, though any temperature below about 65 F will work. Place them in bright, indirect light. An unheated bedroom with an east exposure may be ideal.
Once flower buds have formed (you'll see swollen knobs on the stems), increase watering to prevent the buds from dropping. Flower buds also drop if the temperature is too warm, light levels are too low, or the plant is exposed to drafts. Display the plant where you can enjoy the blooms, but keep in mind that the flowers last longer in cool conditions. The plant moves into active growth after flowers fade. Keep it watered and fertilized from midwinter through the summer. In fall, start the cycle over again. Plants can live for several years in the same pot if the potting medium is well-drained. If the plant becomes top-heavy, transplant it to a larger pot, or remove and root some shoots to start a new plant.