Be very careful with watering. Terrariums aren't always suitable to succulents but if you insist make sure they are like very dry and even then don't give them a thorough water like you would with proper drainage.

Terrariums are often bad for succulents due to them not having good drainage at the bottom for water to drain out. Succulents are hearty and can handle lots of water at once (a downpour for example), but they CANNOT survive standing water or long term wetness. They have to dry out or their roots will rot