As far as I understood, he doesn't have problems making cliffs but raising the terrain near them.
For this, there is tool in FinalSun which flattens ground. (The FinalSun tutorials explain how to use it, but I'll explain it anyway)
Right now I have a cliff like this in my map:

As you can see, the terrain should be raised near the cliffs. To do this, I select the "Flatten Ground" tool from the toolbox. (Before doing this, get marble madness from the link in BlackieChan's post and make sure the cliffs have no errors in them)

When the Flatten ground tool is selected, move the mouse cursor to a cliff. Then start holding the left mouse button and move the mouse cursor behind the cliff.
The point A is where I had my cursor when I started holding the left mouse button. The point B is where I moved the cursor (and stopped holding the left mouse button).

After you've raised the terrain, use the right mouse button to take the tool off.
I ended up with a cliff like this:

It will take some time to learn how to use that tool perfectly, but it's easy when you learn it once