Here are a few I've heard over the years:
1. Never start a story with the weather. This one's nicely exploded by author/editor Roz Morris at her blog, Nail Your Novel.)
2. Never include more than one point of view per scene, and limit these viewpoints to a very few main characters. Funny, how often and successfully this constraint is ignored by many, many authors, including New York Times bestseller (many times over) Nora Roberts, who's been known to sneak in a dog's point of view when it suits her. In my own romantic thriller, Beneath Bone Lake, I wrote one scene from an alligator's POV, and I've occasionally written omniscient scenes along with those where the only human witness is a corpse washing downstream.
3. Never use a sports star or a redheaded man as a romantic hero, and whatever you do, don't have an adulterous hero or heroine. Apparently, (and fortunately) someone forgot to tell Susan Elizabeth Phillips (Nobody's Baby But Mine) and Diana Gabaldon (Outlander) about these restrictions.
4. Never, ever write about a character's dreams. While I agree that this is overdone (especially by beginners) and mostly cringe-worthy, I would never say never.
There are many more "rules" I've heard at conferences and the few creative writing classes that I've taken. But personally, I believe there are only two worthy of your consideration.
1. It has to work. Whatever technique, device, or other choice you make has to result in a reader becoming completely immersed in the story and its characters. Not wrapped up in/distracted by your brilliant wordplay or rule-breaking and not rolling her eyes and groaning, either!
2. Your protagonist's situation must go from bad to worse--at least until the final crisis is met and he/she is allowed to smoke a cigarette, hook up with the love interest, grieve his/her losses or what have you in the denouement.
So what about you? Can you think of any hard and fast writing rules you've been taught that haven't turned out to be so hard and fast after all? Or can you think of any additions (or exceptions) to my two "real" rules for writing?