To get good you need three things: 

- learn the fundamentals 
[composition, balance, unity, white space, contrast, etc]

- practice, practice, and practice [create studies around typography and images practicing various forms of the fundamentals]

- study from life, visit museums [design is everywhere, seek the fundamentals in everything]

i feel like to get really great you need only thing

- really know what you like / what you don't like

creating and destroying; flying cars, roc.camera, july.rocks

That grows with time though no? Tastes change and evolve. So its good to learn more ways to decipher what you like and i think the knowledge of design gives you a wider range in your own understanding.

taste changes, but if you cultivate what you really like and what you don't like as a constant muscle, you'll be good at knowing what you like and what you don't like - the details of design imo - you can learn that anytime with enough time or effort, but cultivating taste is a skill that underpins all imo

the great part is that you can't fake it the bad part is that you can't fake it