I have had a beautiful, healthy Christmas Cactus for years, and years. But it does not bloom !
What should I do ?
Christmas cacti require as much bright light daily as possible, but, as a forest type cacti, they should be shaded from direct sunlight (a bit of direct light is acceptable), so try an east facing windowsill.
The main trigger that gets Christmas cacti to bloom is the short days that initiate bud forming. Ensure a decrease in day length to less than 12 hrs. If your plant is exposed to light in the house when the days get shorter, it might not set buds.
Forest type cacti require higher humidity, so mist frequently. They also prefer 55 degrees to 70 degrees F, (10 to 12 degrees C,) but can tolerate temperatures down to 40F (5C) during their rest period.
Feeding: high-Nitrogen liquid feed 2-4 times a year, before the flower buds start forming. That is, stop at least one month before bud set.
Repot the Christmas cacti when young (use cacti compost), but later repot only when necessary, because the Christmas cacti really do best when tightly potted.
The American Cactus Society: