The tree is interesting. I would go to the file sharing part of the forum. There are lots of TGD files. Take a look at them. It's really the fastest way to learn.
Concentrate on one aspect, like clouds. Good atmospheric settings can give am ok landscape a real boost. The power fractal is probably the most useful thing to learn. Compute Normal also. Use the computer normal for lateral displacements. Go to the node network, zoom in on the power fractal with the lateral displacement. Add the compute normal and connect it to the power fractal.
Read the forums, there are Many suggestions and tutorials.
Happy Rendering!
