This is in the MyPaint wiki, but since some people on here are trying out MyPaint lately I thought I'd point you to my keyboard mapping for my particular workflow:
(Click for larger view. Note that there is a typo in the shortcut image above - "Purer" and "Greyer" have swapped places).MyPaint's default keys are all over the keyboard, focused on the left side. This leads to most often having the keyboard on the other side of the tablet from you, forcing you to reach across in order to press a key. The idea with my setup is to keep your keyboard to the left of your tablet using your left hand to manipulate the program without strain (at least if you are right-handed).
With this setup you don't have to click on nearly any of MyPaint's interface, even color-changing is tied to keyboard shortcuts. One thing not mentioned here is changing brushes by the keyboard. This is default in MyPaint - when you have the brush you want, press Ctrl-[0-9] and it will be saved under that number (so Ctrl-5 will save your current brush so you can get it back by simply pressing 5 in the future).
I usually don't use all that many brushes for a painting, I have 1-6 assigned to the most commonly used ones. I usually work MyPaint in fullscreen mode (F11 and/or Tab) without any of the UI showing.
The keyboard shortcut config file is
here (pastebin). This was originally made for MyPaint 0.9, so not sure if the format is quite the same anymore. To be safe you can just assign the keys manually - it's simple to change your keyboard shortcuts in MyPaint. To do so, just go into the menu and find the functionality you want - hover the mouse over that selection in the menu and press the key combination you want. Done! (this is the same as GIMP's "dynamic shortcut" functionality which for some inexplicable reason you have to activate manually in GIMP these days).
I also import and use
David Revoy's v4 brush kit. There are later brush kits from him, but that one contains a brush I really like (it's the last one in that preview image). Later MyPaint versions can import such kits directly into the program without you having to unpack it or anything yourself. The import functionality is in MyPaint's brush menu if I remember correctly. From the various brush sets, pull together a few you like into the "favorite" set so you can easily find them, then assign keyboard shortcuts 0-9 to them as described above.
My workflow using this setup can be visualized here, along with plenty of annotations and hints (I've posted this video before):
Hope that can be useful for those testing out MyPaint for the first time!
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Griatch