When you’re writing fiction it’s important to keep a few things in mind as you traverse the landscape of your imagination.
Simple story ideas are better then needlessly complicated ones. Too many people lose track of this fact. We see multi-part stories that go many places or maybe even a singular story that spirals out of control with the writer(s) thinking that “more is better”. Take “The Rise of Skywalker” as an example of this folly. I’ve also noticed a lot of modern television stories tell multiple story arcs but often lose sight of the overall point of the story while trying to flesh things out. Why does “Star Wars: A New Hope” or “The Matrix” work? They tell a simple story. “Transformers: The Last Knight” is a disaster by comparison, with seeming to mesh two different plots together poorly.
This leads me to a related point:
Know what story it is you want to tell. Whatever the point/theme/etc. is, know ahead of time where you want to end up or the story will probably be a mess. Again, the Star Wars sequel trilogy (Force Awakens/Last Jedi/Rise of Skywalker) had no idea where it was going or what they were doing with it. By contrast, the prequel trilogy, while far from perfect, knew where it wanted to go (at least in broad strokes anyway).
Every story needs a point! Something needs to change or come of its events. I'm bad at this sometimes too. I’ve also done some serial storytelling in the past where this is a harder thing to accomplish. But at least strive for it in your storytelling. If nothing in your story matters or changes anything, who cares?
It has to make sense! When it comes to TV/movies often times we get stuff that happens for no logical reason. Convenience can be used at times in stories but never really on it as a crutch. If a character acts one way having them act totally contrary makes no sense (even if it might help the writer get somewhere they need to be in the story). This is also true of concepts in general in storytelling (again, this should be obvious but somehow it seems to escape people time and again).
"Show, don't tell" isn't always true. Novice writers are told this again and again but there are varying degrees. Showing you everything with no character feedback or description is bland and boring. The reader isn’t really engaged if they have to do all the work. On the other hand, spoon-feeding them every single point you’re trying to communicate is bad too. A writer learns after a while to try and find a balance. Each person is different and has their own preferences as to what is too little or too much and there’s not really a right or wrong answer.
There are no original ideas. It’s sad but true. You can’t reinvent the wheel. Sorry. But as one writer I enjoy is fond of saying, “it’s not the idea but what you do with it that counts”. You can take what’s gone before and improve on it, mash it up with other ideas and story angles people haven’t tackled yet. A good story is timeless. Something the reader can identify with. A good character is one we can love. Or hate. The ideas are limited but the possibilities are infinite.
There’s almost certainly some other rules I’ve overlooked in this entry. But it’s important to realize that there are rules. You can set out to subvert them. In fact, you should. But you need to understand what they are before you set out to break them. Don’t just depend on TV or movies for your understanding of storytelling. Read a book. Read a bunch. Get out there and see how other people do it and try to decide what works best for your own style. Every new story is somebody building on what’s gone before. Try and seek out the best of the bunch and then try to improve upon them.
One last thing: Try and have fun, no matter what your subject matter. If you don’t enjoy the process, why bother doing it in the first place?