I've read different answers about them eating fruits + veg. but never saw him care much for it. They are mainly insectivores. I used plain topsoil with a small amount of sand , coco fiber about 4 inches deep and moss on top. I pour water directly over all of the moss and it keeps the substrate right how it should be, just by experimenting. It wasn't really hard. It can be fun setting up a naturalistic habitat.
Oh, ETA that there are MANY types of skinks and most are insectivores but some eat fruit + veg, small birds, snails, etc.
There is also type of skink called a gidgee skink that can allegedly live in colonies.