What's Your Unspoken Fanfiction Rule?

Do you have a "rule" when you're writing fanfiction that isn't always conscious or intentional, but one that you find you keep adhering to anyway?

For me, I try not to swear in a fic if the source material doesn't contain swearing. I'm currently writing a Minecraft: Story Mode fanfiction, and I've written a WordGirl fanfiction, and I noticed that, despite usually swearing up a storm in my other fics (and IRL LOL), I didn't in either of these fics. It was just a subconscious thing.

Do any of you have similar rules?