Many agree that following proper grammar and punctuation is a given. Without writing properly in the form and rhythm of sentences, your story sounds flat, jagged, and altogether unpleasant to read. Not everyone is a spelling Nazi, but for the most part, its understood you need to know the English language in order to write. (Or whatever language you write in).
Rulebooks state you should read proficiently. In particular, you should fully understand the genre. For instance, romance demands a formula to the story with an emphasis on the relationship between characters. Science Fiction demands comprehension of the laws of science, while murder mysteries should incorporate an understanding of how murders are handled by the police.
For every rule, however, you’ll find a published author who broke it. Some authors dare to create their own genre, or even publish based on a quirky writer’s Voice. So what does this say about those rules? Some were horrible spellers such as Earnest Hemingway, F. Scott Fitzgerald, and John Keats, among others.
So consider they’re not really rules as much as guidelines. Obviously editors and the publishing industry want would-be writers to submit manuscripts that follow their guidelines, (which are more rules) but there are many factors involved in making a good stories.