Info dumps. I hate them. Sometimes just because the writer knows everything about the world. They are excited to share it and share it and share it. It’s good for a writer to know their characters backstory of every character. The complete history of their world…all ten thousand years of it. It doesn’t mean all of needs to be in a novel. Wait, if a good novelist doesn’t info dump on their reader why would a flash fiction writer? There’s no way it can take place in your story. Limit your info dumps.
Here are other rules for science fiction and fantasy writers shouldn’t break: