Your paint needs to be able to move so use plenty of water.
Paint dries lighter so start with a medium tone and build it up from there.
This process uses a ton of water so tape your paper to avoid buckling.
Use watercolor paper that can handle water.
Using analogous colors will allow the colors to blend better.
Instead use opaque ink or gouache.
Leaving some areas lighter indicates light in the sky.
Instead, use dark colors or even Payne's Gray. This will give your painting more life.
Layers make your painting feel more finished.
Let the paint blend on its own with the water. It will create an interesting texture.
Paint with organic shapes to create a more realistic look.