Depends on the ground you want, desert, concrete, soil sand etc.
I would start with two or three surface layers, each with a different power fractal plugged into the colour channel. Then look at scales, how far away from the ground is your camera. I'm working on a project at the moment where the camera has to be 2m above the ground. In this case I have a combination of Power fractals with scales ranging from 10m lead in to 0.1m lead in and the octaves at about 16.If your camera is higher up you may need to increase the lead in scales. Play with the feature scales accordingly but to start with the default of 1 should be ok.
Use different colour combinations of the same colour range, variations of brown and sand maybe. If you're covering the ground with vegetation you may not need to use any green at all.
Once the ground gets further away from the camera you can start replacing objects with vegetation colours, use a distance shader or simple shape shader to blend between the near surface layers and distant surface layers.
It may be easier to answer your question if you post a link to an image similar to what you're looking for.
Hope this helps
Richard
