I only had a touchpad to work with for this one. The underlying drawing was a pencil sketch I made to show students how to reduce mountains to simple geometric shapes to more easily predict shadows. Even the trees are simple cones. This was the first Photoshop painting I’d ever done. All downhill from there.
Try using texture brushes as erasers to texture the edges of your forms. Paul Lasaine has an exceptionally in-depth tutorial on how to do this. Paul is one of the best in the world (me and my hyperboles, right?), so go check it out.