This is a simple list of rules almost any fiction writer should follow. It's not a complete list, but it is a few points I came up with. You're free to share your own if you want. I think in the end it'd make a nice guide for new authors looking to get published.
1. Just because you're <insert title or degree here> doesn't mean you're a good author. There's a lot more to being an author than a title in front of your name or a plaque on the wall.
2. Just because you think your story is good doesn't mean it is. Always get multiple professional opinions.
3. If given professional advice on how to improve your book, never ignore it. Take it gratefully and fix the problems the professionals addressed.
4. Never assume your book is perfect, ever. There's always room for improvement. There are quite a few 50+ year old classics that are still being edited and improved even today.
5. Always remember to have multiple outside professional feedback readers critique your book. (IE, anyone who isn't family, a friend, or associated/related to you in any way. In other words, complete strangers) When they (and your editor) sign off on the book as being ready for publication, THEN and ONLY then you're free to publish it. Until then, keep working on it.
6. When writing fiction, always remember the rule of balance, which says: For every strength there must be an equal and offsetting weakness. IE, you can't have an insanely powerful monster without some kind of weakness that can be attacked to bring it down. Same goes for the hero or anything. This also works for characters and their traits too.
7. Character balance is important. No living person is totally perfect. Your characters shouldn't be either. They need to have some kind of weakness, character flaw, or other issue that makes them human. Even if they're not human they still need to be "human" in personality or they become impossible to relate to, and will be rejected by readers.
8. If the world you're writing about isn't as familiar and real to you as your hand in front of your face, or your own family, you haven't lived in it long enough, and thus you're not ready to write about it. Writing about characters and other worlds is like writing about your own family. IE, the more you know, the better a story you can tell.
9. Writing isn't about fame and fortune. Writing is about doing what you love and sharing it with others. If you're in it for the money, you're in the wrong line of work. But if you're in it because you love writing, and would do it the rest of your life even if you never made a dime from it, you're in the right field.
Well, that's all I have for now. I'll add more as I think of them, or people share them with me.