There are consequences when you break a writing rule. What a lot of people don't realize is that those consequences aren't necessarily negative--there are postitive things you can achieve by disobeying any particular rule. The key is to weigh the pros and cons and decide if what you gain from breaking a rule is worth the possible drawbacks. Here are a handful of writing rules and why you might want to break them:

Show don't tell - Showing takes up more time and page space. You risk bogging your reader down with unimportant details and harming the pacing of your story by dwelling too long on things that are irrelevant to the plot.

Kill your darlings - This rule should be something more like "be willing to consider killing your darlings." Follow it too closely, and you may wind up removing the parts of your book that made it a story you deemed worth telling in the first place.

Don't use weak verbs like "to be" - To be is what I call a "resting verb". It doesn't take much of the reader's mental faculties to process. Overload the reader with one vivid verb after another, and you might get a comment along the lines of "this is beautifully written, but I have absolutely no idea what just happened."

Don't start your story with a dream sequence - Yes, unless your story is ABOUT dreams and those dreams have real consequences in your story (see, for example, A Nightmare on Elm Street).

Don't use passive voice - Passive voice calls attention to what would normally be the grammatical object of a sentence by turning it into the subject. It's a tool you can use to manipulate which elements of a scene appear most salient to your reader. Just, you know, use it sparingly.