So I have been toying around with material creation for a while, worked through all the official resources (videos, wiki, etc.) and now seem to have hit a wall in terms of progress. While I am able to create basic materials with some effects, I have no idea how to make more advanced stuff (for example post-process materials for cellshading or outlines). I have seen materials for these examples, but their implementation usually goes way over my head without any further explanation.
I do realize that creating materials is essentially writing shaders, which is lots of math and a whole bunch of experience. So my question is basically this: Where do I go from here? Just read books / tutorials on general shader creation and try to implement those in the material editor? Or are there more specific resources which I can use to learn more about material creation?