The first rule of fiction writing is that all rules of fiction writing can be broken. This is also likely the most important. Ignoring the hypocrisy inherent in that rule, it’s in understanding this rule that you discover the difference between someone typing on a keyboard and an actual writer.
To give one extreme example, consider Flowers for Algernon. The style of writing employed, particularly near the beginning, is enough to send an English teacher into fits. Yet the story would not be nearly as emotionally strong or as effective without that particular style. Grammatical mistakes, spelling errors, incorrect punctuation, all the things you were told NOT to do, serve here to actually enhance the story! Or look at Shakespeare, the man constantly came up with words on the fly, never caring whether they were “correct” or not, he just came up with something that sounded good and wrote it down in his plays. You’re not supposed to do that! But he did, and to great effect.
Now, to be clear, this does not mean that the writer now has carte blanche to write in a sloppy manner, throw words together, and then expect to be hailed as a genius. That’s not the way things work. What it means is that breaking the rules can lead to something new and interesting, if the writer knows what he or she is doing. Obviously, that’s the most difficult part of breaking the rules: knowing when and how to break them.
You’ve got to have a purpose in mind for doing so, rather than simply doing so because you don’t want to learn how to do things the right way or because you simply don’t know what the rules are. In this way, it’s also highly important for any writer to know what all the other rules are. It sounds a bit hypocritical to say that, but it’s very important to first know what the rules are before you set out to break them.
So, go out there and read up on the rules, dig deep and see how things are supposed to be done. Then you can thoughtlessly cast them aside and blaze your own trail!