I have a few rules I try to live by as a writer. They aren’t the same as anyone else’s because they’re mine. You may or may not get any value out of them.
1. Never make my protagonist a writer. Clearly, I know what it’s like to be an author, but the idea of making my protagonist one is repugnant. It feels like trying to stick myself in a book, which is not only a gateway to the Mary Sue, but also arrogant and stupid.
2. Backstory must not be infodumped. If I can’t explain some facet of a backstory without throwing a glob of exposition at you, it’s probably not important. If it is important, I can find another way to say it.
3. Avoid the word ‘sexy’ at all costs, unless I’m being sarcastic/humorous. Every time I read ‘sexy’, I cringe. It’s one of those words that almost always gets used to tell instead of show, and the thing it tells is that the author is lazy. I don’t want to hear that her walk is sexy, I want to hear that the subtle sway of her hips with every step draws the eye and stirs the blood. Or whatever.
4. Swearing is best used like jalapenos. I’m not a fan of spicy food. If you are, pick something else that should be used sparingly and for specific effect. Personally, I have no issue with so-called swear words. They have only what offensive power you choose to give them. However, in a book, they stand out for many readers, myself included. When I read a swear word, I notice it. The vulgarity says something in itself, and I feel it’s best to be really sure I want to say that. Usually, I don’t.
5. There absolutely must be some major character for the reader to root for. They don’t have to be the good guy, or nice, or likable, but they do have to suck you in so you care about whether they live or die and succeed or fail.
That’s pretty much it. I follow the rules of grammar (most of the time) and try to offer the best writing I can. Everything else is detail, and usually specific to a particular story.