Kate started this party by asking: What writing rules/advice - whether it was a matter of cannot or will not - have you broken?
Answer: All of them? Seriously though. All of them. Really. Except for the Oxford Comma. I'm a vicious task master with that one.
As my previous blog chainners have mentioned, you should really know the rules before you can break them. For instance, someone who doesn't know any better might use adverbs because they believe that more is better. But as writers we need to know that sometimes adverbs are a crutch used because we couldn't find the right word. Why would you say, "She talked loudly and quickly" when you can say, "She screamed at me in run-ons." Both essentially say the same thing but the first is weak. It doesn't draw the image.
The same goes for prologues. There's nothing intrinsically wrong with a prologue. However too many people use them as dumping grounds for information that should be scattered through the rest of the book. And look at ALL CAPS and exclamation points!!!! If you flavor every sentence with them, they become common, but if you have a book that has just one single word in all caps, then you're breaking the all caps rule and really making that one word special. That can be a powerful tool.
Okay, now what rule do I break often and with great glee? Fragments. I use them frequently. Because most of my work is done in first person for a YA audience, I tend to use fragmented thought. Unfortunately I lean on it too much but the advantage is that when I do use fuller, more complete thoughts, they stand out. Like, "wow, he really thought that through." Plus, I happen to believe that most people don't think in perfectly formed complex sentences. I think we stutter and start and bounce around in our heads.
Okay, like I said, head on over and visit Cole's blog for her answer, which is sure to rock, because that's how she rolls.