cbharadwaj
I know what looks good and I design things that way. If you asked me to explain it and justify my choices, I could, and a lot of people are like "does that really matter?" or "wow, I didn't even notice" when I point out subtle details like leading, kerning, etc. Yes, you could pick up books that teach you about these topics in detail and learn the finer points of graphic design from there, but that won't give you imagination or the creativity necessarily. The spark just comes from absorption. Much like supervised machine learning, you do not learn any explicit formula for doing things, but rather you learn a model based on what you've seen, and you use it to rationalize how future things you make might be or might not be. I realize those sound very similar, but the difference is in that actual "learning process".
I personally think habit will take you further than scientific study in this area. It's an art. The more time you spend immersed in it, the better you'll get at finding what works and what doesn't. That's not to say that there aren't "rules", as in a science, but perhaps they are more flexible than you might imagine. :)