All cacti like bright light, sunshine. Soil needs to dry out between watering. Once it is dry, water it thoroughly so the moisture soaks the entire root ball to the bottom of the pot. Some cacti will use a surprising amount of water in the spring and summer and use hardly anything at all during months with less daylight and cooler nights. In some cases these plants can go an entire winter without using water. When it is difficult to stick your finger in the soil, there are other methods to determine when to water. One is by squeezing the top of the plant, if it is soft and pliable the plant has used it's stored water and needs to be watered again. With this method it is important to know how this same piece of foliage feels when it does not need water. The second method is, if this is possible, stick your finger in the drainage holes at the bottom of the pot. If the soil is bone dry here, you can be sure there is no moisture left in the soil. The third method, if you are very familiar with your cacti, is water it routinely every month to six weeks (This method is the riskiest). Keep in mind that these plants will be potted in a sandy soil, unlike most of your other houseplants. Sand is powdery when dry and holds together when moist.
Pests to watch for are mealy bug and scale. Both try to hide. Mealy bug is a white cottony pest. Scale is a bit more camouflaged. Scale locates itself around the thorns and can seem like part of the plant, but it can be scraped off with your thumbnail. Treat the pest by spraying with oil soap, or diluted alcohol. Because cacti have so few leaves you can also use a scrub brush and physically remove the pest.
Remove any rotting stalks. These in the beginning look black and feel soft and in the later stages they are hard and crunchy, sort of petrified. Cacti can be pruned back but they scar easily so make your cut at an unnoticeable angle inward and out of sight. Branches will not emerge from the sight where the cut is made. Cacti grow slowly.