Some suggestions:
- Add some big rocks in your scene as well
- By adding some stones you could add some gray-ish colors to the mix.
- Perhaps add some small vegetation to the rocks surrounding your scene.
- Include some wooden crates or perhaps some remainings/debris of an old (wooden) fortress
- On your landscape you could paint remainings of a river that dried out
- Add an old water well that was used by peasants in the past to fetch water
- Some remaining of an old civilization like caves, statues or something
- Not sure why there are so little or no shadows in your image. Perhaps your turned them off for the screenshot but make sure there’s more shadows in your scene as it provide depth and makes the 3D stand out more.
In my opinion good level design should tell a story by itself based on the type of props you use and by the way props are laid out in the scene. It should not only be a placeholder for your gameplay but also be part of the storytelling.