I find someone to pay me to build something using it. It's how I learned jQuery, Sinatra, Bootstrap. Bout to do the same with Angular and Rails.
I wish I could learn a tech from a book, but the signal-to-noise ratio is generally too low in the vast majority of books I see. I don't need a bunch of "recipes" or a disgustingly short bash rundown in a book on Ubuntu, I need clear, server-oriented insight into how the OS internals work, and what went into the underlying design decisions.
Every book on a programming language I pick up spends 90% of the time on basic stuff you could pick up in a few hours with the same language's "getting started" page. I'd love a teardown of the source code with commentary on the intentions of the language designer. I don't want a gentle introduction, that's just a waste of my time. I've already introduced myself with a dozen or so hours of playing around and reading docs. But the people that could write useful things about technologies generally aren't. Or maybe I'm just not looking hard enough.