I think "build something" would be better reworded as "do something;" that is, use the technology. Studying theory before diving in may work for other fields but if, say, you're trying to learn Django, you learn more from making a web app with it than you do from reading or watching several tutorials or guides. If you want to use vim, just write your next program with it, and consult the help every time you notice an inefficiency in your work flow.

I think this approach works with hacking because there are so many little perks you have to know about and finishing a project is one of the best ways to expose yourself to many of them.