Very nice color palette! The foreground dune which dominates the shot is shaded very efficiently, it looks really good, and there's no denying that's sand. Tops on that.
The midground dune looks really good, of what we can see. You did a great job at making it seem like it's waaaayyyy back there, and you were wise to make it a much lighter hue than the dune in front of it. My only problem is that as you follow it from right to left, it just kinda drops off and ends behind the peak of the foreground dune. If it had continued going, flat as can be, to the other side of that peak, it would've been stronger in my personal opinion.
The clouds look fantastic, almost oil painted...that sky is truly a thing of envy. My only other negative criticism is the yellowness of the sun, but take that particular critique with a grain of salt; every artist does things their own style...so your sun happens to be yellow. Happens to be spiky. Happens to bleed out a yellow aura around itself, and that's totally acceptable. If it were me, and the sun HAD to be in the shot, I'd make it a diffused white orb. But like there's no mistaking that's SAND that you've drawn there, there's also no misconceptions that the thing in the top left is absolutely the sun.
The positioning could also be improved...like, making it not cut-off into the corner would've lended some additional strength too. I want you to google or wikipedia research the "Rule of Thirds" which is a very strong and important rule of thumb when it comes to composing your art. It would really hold you over to implement the Rule of Thirds in the future. That way the frame, in it's entirety, really pops and nothings cut off.
You're doing great, man! Never stop!