Leo Horie's documentation and tutorials for Mithril are one of the best examples I've run across of truly stellar documentation. Not coincidentally, reading through it all, you learn a lot not only about the library but also about good programming techniques in general.
In the same vein, there's React-DND by Dan Abramov. The tutorial is probably one of the best React tutorials out there. It teaches good ideas about how to architect your app (think about state etc.) apart from how to use the library effectively. Highly recommended for anyone who's working with React.
I don't know how Leo leveled up, but really, there are two things you need to do to improve your style:
Figure out what to practice, then practice :-)
That's what I'm currently doing with j2c, a small js library.
After writing the core (JS object to CSS compiler) in a couple of evenings, I decided to play the open source game, polish the API, bullet-proof the test suite and write good docs. That took much more time, and I'm not fixed yet on the final API.
