It's always the same technique: take a small fuzzy eraser brush, and do some curves in the grass layer's mask (or the grass itself). Don't forget to do the same thing on the texture of the grass, too. If you are following RobA's tutorial, that is. In that case, you should also erase the "seashore" layer, which, since it only has the sea mask, covers the entire land, even if you don't see it. Another thing I did is do a special texture layer for the rivers, with highest detail and size, to have some variation; to make it so it's not too apparent, I just put opacity down on the "river texture" layer.
Originally Posted by The-Somberlain
If you want, you could also use paths, and brush black on the grass mask using "trace path", then the paintbrush with, again a small fuzzy brush. However, It gives you less freedom, as using this, you'd have to tinker for hours to try and get that path just right, while with the eraser you can just start over and get a good result after a try or two. I guess it's even easier if you have a tablet, which I don't.
RobA: you mean, put a title in the post in this thread, or create a new one?