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It's a cactus, so it should be easy to care for – I just water it sparingly and keep it dry, right?  Wrong. 

Whether you have a Thanksgiving or Christmas cactus (or an Easter one, for that matter), you take care of them the same way. Keys to their care come from their native habitat, which is not a desert but the cloud forests of costal southeast Brazil. The high-altitude costal areas where they're from are cool, shaded, and relatively humid with the mists and moisture rich air. They are epiphytic or lithophytic – meaning that they grow on trees and in crevices with decaying plant material rather than in the soil. And while you don't need to know this to grow them, the morphology of the flowers have developed to support the feeding of hummingbirds which act as their main pollinator. 

Since we don't grow them epiphytically, when we pot them we need to make sure that we provide a light substrate for them to grow and to get plenty of oxygen to the roots. Potting mixes should have a high ratio of peat or coir and even some bark or other coarse woody material.

As for watering, you'll want to keep the soil fairly moist, rather than dry. You'll also want to let them dry slightly between watering, but don't think that they like to live the life of dehydration - you do need to keep them watered. 

One of the reasons that they bloom at very specific time of year has to do with light and, to a lesser extent, temperature. They are short-day (or rather, long-night) plants, so they flower as days grow shorter (or longer, in the case of the Easter cactus) and nights grow longer. The Thanksgiving cactus will bloom with just a little shorter dark period than the Christmas cactus, which is why it blooms in late fall, as opposed to the Christmas cactus that blooms closer to when days are the shortest around the solstice. They will also bloom better and longer if they have cooler temperatures, so keeping them in a cool area of the house is ideal  In high light situations the cladodes will turn red. Keeping them too dark, however, will limit growth and keep them from thriving. 

Since they are short-day plants, the plants need a period of several weeks where the period of darkness at night is 12 hours or longer for their flowers to begin forming. This occurs naturally about mid-October, but you can delay flowering by using grow lights to lengthen the day (or keep in mind that bright indoor lights can also limit or reduce blooming). Also, don't be alarmed if they bloom at odd times through the year. Since daylight coming into your windows can be altered by window treatments or films, the light levels can technically be just right for flowering at multiple times per year.

In my old office, the tint on the windows created the right conditions at least once or twice per year – one year I had a Halloween cactus and the next it was a Memorial Day cactus.   

If the cactus does not flower, you need to move it to a spot where it gets at least 12 hours of relative darkness to initiate blooms and keep away from indoor light sources or windows near outdoor lights. Hopefully, you'll have lots of colorful blooms for Christmas.....or whichever holiday your cactus celebrates.