You have to know the rules to break them. I've addressed this bit of conventional wisdom before, but my thoughts have been refined on this point.
You do not, strictly speaking, have to know the rules first. What you need are two things: a grasp on the problems that are solved by the rule, and another solution to those problems.
The rule of thirds is truly about placing things off center, to create a livelier visual result. Various rules about portraiture are, mostly, about creating a flattering look, avoiding making the subject's nose look too big, and so forth. Perhaps your approach to portraiture plunges the nose into darkness, so it's OK if it's too big. We focus on the eyes, perhaps, because as animals we're most interested in the eyes of other animals. By creating or observing an equally interesting element, we might focus on that element instead of the eyes -- the main thing here is to not focus on something random and uninteresting. And so on.
Knowing the rule, therefore, is perhaps nice, but knowing what problem the rules solves is essential. You might well grasp the problem without knowing the rule in the first place.
Solve the problem, don't worry about the rule.