New sketch looks good, glad to see you keep working on these.
To improve on this, try and use a wider colour range. At the moment, this all looks very monotone, with just varying values of one colour. If you study desert photos, you actually find a whole range of colours in there, like this:
Notice that there are different hues in even in just the sand / rock that is in the same light, but you also find cooler shadow tones, and the blue atmopsheric perspective permeating into the distant hills.
It would also help to create more variation in the layout of the terrain. At the moment it looks totally flat with rocks just sticking out, but if you make some natural undulations, hills and folds in the landscape it will seem more real. Very flat deserts do exist, but for the purpose of your work I would be tempted to make more interesting terrain. Some vegetation to ground it in reality would probably help too, and will enhance your scale.
Finally, try and use more confident and opaque brush strokes. Using opacity settings on your wacom is great for laying things, but can cause things to look a bit washed out. Try using harder brushstrokes and more hard edges, I think it will help a lot :)
Hope that helps, look forward to seeing more soon!