This technique is meant to give your flat, lifeless plateaus and hills a nice subtle rolling-hills effect. here is some pictures of the map i will work on:
Now, go to the elevation layer, select the Heightmap editing tool, and pick one of the Peaks brushes. Set the strength to about 0.05 and the size to 40, like this:
Now, go around brushing the map with it, going for only a small, but a very rocky elevation increase.
Then switch to the filter tab and select the Unsharp128 brush. Set the strength to 1 and the size to whatever is necessary to reach all the areas that you "rocky-ized" and blur them until stuff is able to be built on them (you can find this out by selecting View > Debug > Slope, the green color is what you can build on).
Now, your terrain looks much more like real terrain!
The whole map when i am done:
the slope data when i am done: