Well, I'm far from being as knowledgeable as some folks on HN, but have a lot of factual knowledge about odd things. My only advice is curiosity and reading, notably about "real" subjects. That could include well written fiction. I don't plan to read about specific things, just let my brain be filled with lots of stuff.

Also when you see old people doing interesting work, talk to them if they don't mind it. At my current job, I made a point of talking with the old-timers about the technology, and gained a lot of practical knowledge that would otherwise be lost.