Little key shaped, mostly transparent so I can still read the key underneath, stickers that give me some hinting as to what keys did what in combination with alt clt and super.
I thought of this when I was using my wife's desktop the other day and she has put the Gmail keyboard shortcut stickers (provided by Google at one point) on her keyboard as a learning tool.
I'm never going to remember all the useful shortcuts exposed in Gnome shell just by reading documentation. Not going to happen. And we've got no hinting in the UI itself for a lot of these things at the moment. And that isn't a knock against GNOME3 specifically...its the nature of the beast. Applications with drop down menus will try to give you hints about accelerators..but there's a lot of stuff that predates G3 Shell where the keyboard interactions aren't learnable through use. If the GNOME designers find a way to solve that problem, then bonus points for them. In the meantime, training stickers on my keyboard are the best idea I can come up with for my own needs.
Now I can of course do up an inkscape svg template for these things and share it with people. But if anyone else is already looking at doing this sort of thing...let me know.