The rules that guide realism are plenty. The rules that guide imagination are not that many.
When you're aiming to bring realism into your art, you must be observant, perceptive, and attentive to detail. Beyond that, you must be meticulous, thorough, and especially sensitive to what is off. When you're aiming to bring imaginativeness into your art, you must push boundaries, roam, distort, convert, complement, adorn, and go on your whims.
Will your imaginative work of art have any coherence to it? If you want it to. Many can appreciate that though the absence of it can also be valued. That "on-drugs" kind of freedom that unleashes possibilities. Will your realistic work of art have any fanciful touches? If you want it to! That would be delightful though the absence of them can also be impressive. That "where's the lie?" effect when it is so close to reality that it might as well be.
Nevertheless, being somewhere in between can make for great, astounding art, too. The type that could bring reality to imagination and imagination to reality - literally.