...don't break them.
When we were little, a good number of us probably wished we were older so we could make the rules instead of having to follow everyone else's. ~huff~ ~pout~ ~scowl~ As SFF writers, we make 90% of the rules. Our worlds, our magics, our weirds. That 10% we don't break are the genre expectations that are part of the writer-reader Contract of Expectations.
So what about that 90% that is within our grubby little grasps? I can't say it better than James did yesterday, so go read his post.