There are particulate and non-particulate substrates. Particulate substrates consist of multiple small particles and include sand, corn cob, walnut shells, and rabbit pellets. I do not recommend corn cob or walnut shells. Corn cob is not digestible and is large enough to create impactions, requiring surgery. Walnut shells are also not digestible and have sharp edges.
Many people use sand and many use rabbit pellets.
The advantage of rabbit pellets is that they allow the dragon to dig, and are safe, and even nutritious, if eaten. I use paper towels for young animals and for animals with parasites, since it's so much easier to keep the enclosure immaculately clean. Cleaning You need to both surface clean and disinfect your dragon's enclosure. To clean off dirt and feces, use a mild soap, such as Simple Green, and water mixture. After surface cleaning, you will need to disinfect it.