Ok, here's how I make terrain.
First I create a brush with a size of the area I want to create and texture it with BEVEL to decrease the amount of clipnodes:
Then I clip it into multiple triangular prisms:
After that I enter VM and start dragging verticies vertically:
When I'm fine with the results I start to texture it. First I apply the texture I need to the ground:
Then I select the face I applied the texture to and press Shift+F6:
And I start left-clicking on the ground faces applying the texture to them:
After that I do the same with the cliffs:
I scale up the cliff texture a bit to get better results:
Then I again use Shift+F6 to apply the cliff texture:
There's a screenie of what you can make using this method:
