Although some morning or late afternoon sun is perfectly fine and probably appreciated, your Christmas cactus doesn’t need the intense light that desert cacti do. It likes a bright spot on a windowsill, but indirect light is mostly the way to go.
Although they do have the capacity to store some water in their fleshy leaf segments, Christmas cacti aren’t quite as efficient at this as their desert cousins. Don’t let yours go without for too long, or it might turn wrinkly and even start dropping foliage.
Christmas cacti really aren’t too fussy when it comes to soil, although it’s a good idea to keep in mind that they’re naturally epiphytes that grow on trees rather than in soil. They like a mixture that’s relatively loose, but does retain some water.
You can fertilize yours once a month or so during the growing season (from early spring through late summer), but make sure to stop once you see the buds start to form in fall.
I’ve never pruned any of my Christmas cacti: the longer their stems get, the better they look to me. If you do want to shorten them at any point, it couldn’t be easier, as you can simply pinch the segments loose.