Instead, I've decided to make a compilation of different tutorials and charts that I personally use to learn how to paint.
The most important thing you need to learn even before starting to read a tutorial is that all walk-throughs are meant for you to understand how things work. My point is that after reading and later practicing a tutorial called 'how to paint a glass duck' you should be able to paint not only a glass duck but also anything else made of glass. You should concentrate on understanding the rules and patterns instead of trying to copy what you see on the image. Otherwise you'll end up knowing how to paint only a few things from only one perspective and one lightning pattern.
Hope you find my collection useful!