One rule of thumb in writing, particularly in fiction, that I adhere to is learning structure in writing. Would you trust a doctor to operate on you if he/she didn’t have a working knowledge of anatomy? Well, I liken that to writing – structure, structure, structure. Once you learn the elements of dialogue, narration, point of view, description, setting, time & place, etc. and the balance between all of these elements, you are off to a flying start whether you write non-fiction, literary or commercial fiction.
There are visual images that need to be addressed such as white space on a page. In today’s world, there is a greater push for white space (tends toward commercial) rather than dense words on every page (tends toward literary). Again, balance enters into this. Think of your audience. If writing more commercial fiction give your reader more white spaces, less description. Even in literary pieces, people raised on speed in computers, texting and iPads easily tire of long passages that go on and on about the landscape. Readers like to get to the story quickly and absorbed in the conflict that ensues whether it is physical or psychological or both. And don’t forget CONFLICT! That is the heart of your story.
There should also be adherence to reality – what motivates people in real life and how does that translate into fiction. Study human behavior for an understanding of human behavior even if writing commercial fiction.
That is not to say you can’t experiment, but you need understanding of structural elements in order to innovate. Like great artists who have gone experimental, almost always they can do realistic work first. Picasso did realistic portraits before his famous bombastic pieces.