During the fall months your Christmas cactus will set its buds for flowering around Thanksgiving (sometimes sooner) and this is the crucial time for getting blooms and keeping them from falling off just after you see them form. There are three reasons the buds fall after forming; over-watering, lack of humidity and lack of light (especially inside the house). If inside the house, place an over-sized saucer filled with pebbles and water under your cactus plant. This will increase your humidity. Keep the water low enough that the pot and water do not touch.
It is a better plan to keep your Christmas cactus outside as long as possible as the cool nights actually cause the buds to form. Try not to allow the temperature to drop below 42 degrees however your cactus would probably be all right if it did. Once the need for bringing it into the house arrives, place your cactus in a spare bedroom by the window and just like the Christmas poinsettia, do not turn on the lights after dark. Poinsettias and Christmas cactus need 14 hours of total darkness each night in order to bloom. This "short-day" treatment starts on the first day of fall, usually September 21 or 22. The difference between the poinsettia and the Christmas cactus is that the cactus tolerates cool temperatures but the poinsettia does not. Another difference is that the poinsettia likes to be watered regularly and the Christmas cactus prefers to be dry. The real secret to growing Christmas cactus is to ignore it most of the time.
When you see the buds, be careful not to over water. It is best to go a couple of weeks between waterings and allow them to dry out. When you decide that they should be watered, water thoroughly at a sink. They should never sit in water. As soon as they are finished blooming, ignore them for at least 30 days. That means no water and certainly no fertilizer. Try to place the plant in a cool room, somewhere around 45-52 degrees such as a sun porch or a basement window or in a garage window that is kept cool but not freezing.
March would be the month to do any pinching or pruning and also to start watering, but not a lot. Give it one good drink, then, hold off for 2-3 weeks between waterings.
As we get into better weather and more sunshine, you may increase the water and add some fertilizer. Also, increase the temperatures into the 60s. This would be the best time to re-pot, if you feel the need to re-pot, but remember that Christmas cactus' like to be root bound and will actually bloom better if the roots are in a tight space.
Your Christmas cactus loves outdoor conditions and especially the cool nights. During late spring and all of the summer months place your cactus outside in a bright, but not direct sun, area. Water occasionally but still allow it to become pretty dry between waters. Maybe every 10 to 14 days as opposed to the usual once per week or even daily waterings, which most plants need during the hot summer days.