Now it's time for the soil. Have an idea of how you are going to place the plants inside the jar or bowl. Keep in mind the plants will grow, so you don't want to jam them in the container too closely. That way you won't disrupt the arrangement trying to maneuver plants into difficult places later. After the plants are in, you can add tiny decorative items and figurines to create a theme for your terrarium.
Small mirrors give a nice pond effect, or try constructing a path from colored gravel.
Keep the finished terrarium out of direct sun or you'll overheat the plants inside the glass. Bright, indirect sunlight is best. You shouldn't have to water very often. You'll water the plants initially, and then moisture will recirculate inside the container in the form of evaporation. That's all there is to it.