A cactus is a unique plant that is easily cared for even inside your home. For this reason many people with a green thumb and even those who are serial plant killers purchase cacti. Follow these steps to properly care for your indoor cactus plant--no matter the type.
Pot your cactus in a clay pot that is not glazed. Select one that can be drained easily through a hole (or holes) on the bottom.
Add a potting mixture made of orchid bark, pearlite, potting soil, peat, coir, pumice and/or oak leaf mold for the best results. It's a good idea to repot your cactus approximately every two years shortly after it blooms (if it is a blooming plant). Leave about two inches between your potting mix and the top of the pot if your cactus is expected to grow.
Water the cactus approximately once a week. In colder climates (such as during winter) you may need to water your cactus more often because the heater may use some of that moisture from the plant. Test if your cactus needs water. Measure the top 1/2 inch of soil with your finger and if it's dry, water the cactus.
Pour enough water to the point that it begins draining through the bottom of the pot. When you want to reduce the amount of water a cactus is getting, extend the time between waterings, instead of the amount you use when you do water the plant.
Place the cactus in a well-lit area. With an indoor cactus it's unlikely you'll find a spot that has too much light. Great places are a bay window, an atrium or a bright entryway where other plants may get damaged.
All of these steps are general rules to follow. If care instructions come with your plant that are different than these steps please follow those instead if they are different or use these steps to supplement unclear instructions. If you want to you can add fertilize such as Miracle Gro or Osmocote to help you cactus thrive.
These steps are for an indoor cactus. Steps will vary for a cactus being kept outdoors.