I've had to impose this rule on myself: when the first draft of a story is finished, go through and un-italicize at least half the italicized words. And then go back and un-italicize half of what's left. You would gape at the number of italics in my first drafts, I'll tell ya.

And as far as rule-breaking, my rule is: Learn the rules, and learn how to write within them. Once you've done that, you can figure out when it's necessary to break them. Being conscious of the rules makes you realize when you're breaking them for the right reasons.