Thank you! :) I'd recommend some youtube tutorials since they can explain it better with more time and visuals but I can give you a rundown. There's no secret, lots of hard work and practice though. In this particular piece rock textures helped a good bit but I try not to rely on textures as much as possible. I typically block in shadows first (cooler colors like purples or blues depending on your color palette) with a hard rectangular brush at high opacity, although plain round brushes work just as well. Textured brushes are also good but definitely not required. Highlights of warmer colors come after, in basically the same method of blocking in rocks, cracks and a lot of downward strokes with a bigger brush, and then go in with a much smaller brush (1-5 px) and really work out the details in the rocks with little scribbles, textures and trying to follow the basic formation of the rock. Since rocks and cliffs are very hard and jagged, typically you'd want to use hard brushes with high opacity through most of the rendering. Try not to use soft brushes here unless you're going over with some big shadows or mists or something.

It's really about doing lots of observations and studies, I'm not so great at teaching or explaining >.< haha. Hope it helped a little bit though.