The archetype here is the woman alone in the house who hears noises in the basement and goes down the dark stairs carrying one small, flickering candle. Nothing is quicker to annoy editors than main characters who do nothing and simply get acted upon by the plot events. Worst of all is the main character who gets yanked out of the monster's grasp by some last minute rescue that comes out of nowhere. Deus ex machina endings might have worked for the ancient Greeks, but modern editors despise it. Make your heroes and heroines solve their own problems, or at least die valiantly in the attempt.
Nobody wants to read about a witless wimp.
Media-based settings or characters. Unless you have a contract to write a Deep Space 9 novel, for example, or a specific invitation to write in someone else's universe, do not use copyrighted people, places or objects in your writing. Remember, you want to become such a terrific writer that someday they'll be making movies and TV series about your characters, the ones you made up all by yourself. Well, a story that does nothing but repeat the same tired old mistakes will have nothing in it to make it stand out from the other five hundred stories the editor received that month. That tells the editor three things about that writer.