What's the answer to knowing good art?

Expression is the key :D

Explanation:

Art is a mirror that reflects the harmony and balance in the universe, you can't just 'know' art, you need to feel it. Art can take any form to express how you feel on paper, if you're sad, you'd probably use dark colors, or make sad portraits or whatsoever. If you want a literal answer, you must understand the basics, let me remind you, even the most basic art form can prove intriguing :D

Just know your style, like every artist does, that, would be your new identity :)