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.
