Pour the potting soil into a plastic or clay container that has a drainage dish beneath it. If using a plastic container, consider spray painting it with Krylon Make it Stone spray paint for plastic that will allow you to paint the plastic pot with a faux stone surface that will give flair to the decor of the pot. Glass containers are not recommended for cacti.
Place some sand, if desired, on top of the potting soil. The sand needs to be appropriate for cacti. Do not use sand that you have picked up at a beach or park. These sands have contaminants and will not be healthy for the terrarium.
Plant the cacti into the container carefully. Do not plant them close together and overcrowd the terrarium. Overcrowding the terrarium will not allow proper breathing or growing room for each individual cactus.
Arrange the stones and the decorative pieces in the pot. Do not overcrowd the terrarium. Decorating it with natural stone will give it a more realistic feel. Using stones that are odd in number will be more pleasing to the eye. Some decorative touches to add may be tiny plastic scorpions or lizards purchased at aquarium or pet stores.
Place the terrarium in a location that receives sunlight.