Pay attention to shape.
Shape shape shape. Foreground and background, and the harmony between formations. I know landscapes in real life are all over the place, because they can do what they want, but unless you're THAT badass, and on a godly level, if you're drawing your own landscapes, you want to make sure you got a good composition.
I'm sure Cype can help you with this better, cause this is his specialty. But basically, do little thumbnails to help you out, and don't just jump right into it.
Use to start off, so you can focus more on formation, shape, and compo.
Something like this, for example.

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