One thing that the Eriond tutorial does is to incise flow to run rivers. You can also use Wilbur's Texture>>Other Maps>>River Flow tool to create a river map that you can drop on top of the terrain without having to carve the deep canyons all the way down to sea level. Learning the correct settings will take a bit of practice because the tool's effects vary a bit with the resolution of the image. More precipiton erosion will reduce the hard edges from the masks.