On a large scale, it's just basically reading, reading, reading. Absorb through your eyes and ears at every opportunity.
Imagine putting together a jigsaw puzzle. In order to finish the puzzle, you have to find the corners, the edges, and sort pieces by color or pattern. It's the same for learning something, except it's a 30,000 piece puzzle, and you can't see the puzzle (you aren't able to quantify what you don't know). Through listening and watching and reading you learn to see the corner pieces, and the edge pieces, and you begin to see how things fit together slowly over time. Little patches here or there become clear, and you just fill in the puzzle as you go.
Unfortunately, you'll have to focus on a region of the puzzle and not the whole thing, because a 30,000 piece puzzle is a very large puzzle, and no one person can put it together in their lifetime. This is why specialties exist in engineering, and even within engineering disciplines.
On a small scale, just absorb any information you can find on the subject(s) you're interested in, any time you can do so. You'll soon find out whether or not you're really interested in the subject, and if you really are, you'll start to get annoyed by your human body because it can't take information in as fast as you're ready to receive it.