You have the right approach with the two dunes on the top-right. The two on the left are unreadable. All you need is shapes & light - if you focus on details during the construction stage, rather than shapes & light, it won't work out.
Where there are no dunes, you can just have shallow slopes - slight changes of value.
Here's a favourite of mine.
I like the design of the ostrich. What you've done on the legs & neck they call selout (search the forum), & I personally don't favor it. It's the process of placing AA flawlessly but then undermining it by using the wrong values for some reason.
I'll follow this piece's progress with interest.