Deserts are wastelands: I associate them with lifelessness, depression, boredom. They are also timeless, stretching in all directions, where the horizon is the same wherever you turn and look.
Deserts in dreams often give me a sense of the purposeless future.
However, deserts are never as dead as they first appear. Sometimes they have flowers growing in them, or bookcases, or people.
They are also associated with exotic places, and movement towards them.