Thanks for all the ideas and comments. I've continued the work on the desert and have tried some different things, not all being great. One of the things was to add some craters in the south west part of the desert. I actually took some pictures of the moon and cut out the craters and put them in the map. I'm also experimenting a bit with different colours, I'm looking at making some part of the desert more redish like mars, and some part black (like a desert of death and pain). I'll see where I end up.

At the moment I'm having a break from the map though. I bought Blood Bowl Legendary Edition so I have to play some more before I continue on this ;-)