Dunes and dots is how I've always done it with an oasis here and there and some camels and pyramids - you give the brain some cues and it fills in the rest. You could use some little cacti, cracked mud, or craggy mesas for chaparral areas (American southwest). Craggy and folded hills like the Badlands of the Dakotas. Volcano and lava field would also work. You'd have to practice drawing those on scratch paper first.