This one was fun. Modelled it following Jonathan's course (highly recommended!). I was a bit greedy and wanted to try a procedural desert using Cycle's experimental displacement treatment but had too many problems aligning it and making it look right, so a final plane it is. Maybe I'll come back to this one some time later down the road and try and make the scene a bit more interesting.
It's looking good. With time and practice you'll get the hang of lighting and materials. Also there's a course on creating sand dunes:
https://cgcookie.com/courses/creating-procedural-sand-dunes-with-blender-2-8
As a note, I had a TERRIBLE time rendering this one, as the light on my final render was way over-exposed, looking completely different than the render view on my viewport. I tried everything, from handling the strength of my HDRI, to editing the World directly on my shading space with math nodes. Nothing seemed to work. Ultimately settled for bringing the exposure down on my render properties (it's on 0.3 and you can still see it's slightly burnt!) but I'm curious if this was a bug or if I did something wrong.
Maybe you can use shader node "gamma" to adjust single object, or use compositor.