So I finally made a tutorial. o/
I really hope that it's understandable. I tried my best to make easy to follow. If you have any questions, feel free to ask me.
Here's some shortcuts for the tools I used to help you work faster:
Toggle transparency: -
For the brushes, Some of them don't have shortcuts. You can set the shortcut you want, just right click on it then 'options'.
The work used in this tutorial:
Some of my work that I used this technique on:
And you can see the others in my gallery