Author has written 28 stories for Harry Potter, Chronicle of the Black Company, Tangled, American Gods, Avatar: Last Airbender, Greek Mythology, Lord of the Rings, Cthulhu Mythos, Starship Troopers, Pokémon, Hunger Games, Lost, Battle Royale, Red Dawn, and Batman Begins/Dark Knight.
Rules for writing that I've taken from other, better writers, or that I've learned the hard way:
1. Any following rule may be broken under the right circumstances.
2. If your story has an antagonist, then for god's sake make him feel like a threat. Nothing's more boring then being unable to imagine how the hero could lose.
3. Don't be afraid to do horrible things to your characters. If everything is going fine in the hero's life, then you're doing your job badly.
4. Clarity is essential. The audience doesn't comprehend what each character wants, what obstacles stop them from gaining it, and what they're doing to succeed anyway, the story is much harder to read.
5. Don't hesitate to blatantly steal from other, better works. If there's a plot element an episode of Avatar: The Last Airbender that fascinates you, then feel free to use implement it in your story about Doctor Who fighting the Cybermen. Hell, Shakespeare wrote perhaps one original play in his life, but he still did a bang up job, because he took older stories and made them his own.
6. Allow the plot to build before the climax. Imagine how boring Lord of the Rings would be if Tolkien had gone straight from introducing hobbits to the Crack of Doom in 1,000 words.
7. Each character should have a different "voice", or "world view". If the hero, the villain, the sidekick, and the love interest all witness the same event, they should all have different reactions to it. It makes the story more realistic, and more interesting besides.
8. If you have writer's block, stop writing- it's your brain trying to tell you that it's running on fumes. Continue thinking about the story, though, and pick it up again later. I've found that switching projects every time one runs dry works pretty well.
Just in case you ever wanted a first hand account of a war in Afghanistan: