- Mix a brown color like Graveyard Earth* together with water in a 2:1 ratio and paint the entire hill with two layers.
- Once it has dried up, take a lighter ochre-like color like Bubonic Brown and dip the brush in it. Then dust off the majority of the paint on a towel until the brush gives off a very weak trace of paint.
- Brush the paint lightly over the hills and notice how only the higher points of sand gets covered, leaving the darker earth color shining through from underneath.
- Hopefully, this should make it look like dirt on the ground. If you'd like, you can use other colors on top of this basic surface to make sections of stone or other vegetation.
This is how my hills looked after this stage:
* I use the landscape set by Games Workshop, containing a large pot of dark brown and a smaller one of ochre brown, as well as glue and plenty of flock. It's a quite expensive set but overall a fairly good deal.