Succulents and cacti are currently incredibly common houseplants. However, the term succulent is not a scientific term. It is simply a broad term used to generalize fleshy plants that have a high water content in the leaves, stem, or roots. Due to the wide variety of the category, their histories and backgrounds are diverse. Cacti can come from all over the world and different elevations from being on some mountains to truly being in the desert. While the advice listed below is overall useful and accurate. It is important to note each individual plant comes with its own needs and the care required may vary from plant to plant.
The most important thing to note is that that succulents and cacti tend to need more water than most people think they do. While many people will think that you can go weeks without water them (which is true), this is not the environment that they thrive in and they will definitely not grow if they are lacking water. Instead, ensure that your pot has draining holes and then watering it until water seeps from the planter. After this, just wait until the soil is dry again. In the growing season, this can be as often as once a week which is much more frequent than the assume 6-8 weeks. During the cooler seasons, the time between can extend a bit as it tends to be cooler outside and the plant requires less energy to survive.
It is worth noting that while these plants are adapted for the desert, they are also prone to sun burning. This means that prefer southern windows and less direct bright light. However, they can be trained to accept bright direct sunlight by slowly introducing them to the change in lighting.
One final note is that succulents can often be propagated to grow new plants. It varies from plant to plant, but generally it involves cutting off a leaf, placing it in water until you grown new roots then plant! However, as with all of the advice in this post, make sure to check the requirements of the exact plant you have before attempting this.
The Plant Basics 