Grammar, research, and prose are all important factors needed when writing a fiction story, however, I believe the best component for a fiction story is one's imagination. As an avid fiction fan, I've had multiple moments of escaping into the writer's imagination. I've done this so often that I've envisioned myself living in the writer's world and interacting with the characters of the story. To be completely honest, this was based on my effervescent need to escape from any responsibility I had at the time --- but that's neither here nor there.
The point remains that a great imagination can expand your fiction writing to extraordinary lengths!
Based on personal interactions with fiction writers, I always hear two concerns form them; "I can't think of a good story" or "I've tried to write a story like... but it just didn't work". I always find these misconceptions disheartening. Whether you're a writer or a plumber, you use your imagination every single day. Think of the last time you've envisioned a scenario in your head. What happened in that scenario? Were you fantasizing about what you were going to cook? What you wanted to wear the next day? Or were you simply envisioning that less-than-great moment of getting out of your bed and going to the restroom at 3 in the morning? That's it! That's your imagination! Though, I'm sure, you wouldn't want to write about using the restroom to your readers... (unless that's your thing, no judgement here) but these vital moments may erect a story, an idea, a concept, or an over-exaggerated moment that may become the greatest fiction writing of all time.
Developing a plot is another difficulty many writers have when writing fiction. I must admit how easy it was for me to write my story of stopping a space-time continuum or the story of the invading flying plates once my plot's been chosen... (there's a reason why I'm just an avid reader). However, a stories overall concept can be written from any source of one's imagination, you don't have to pressure yourself into finding your plot before beginning your story. For example, (and yes, back to the 3 a.m. restroom call) if you were imagining yourself going to the restroom at this time, why not make your character do the same? You can ask yourself, where is your main character's location, what is your main character doing in the restroom, and why does the reader need to know your character's whereabouts at this moment? Asking yourself these questions and raiding your imagination can give you your main point -- your plot-- what your story is really about!
Another common issue with writing fiction is the need to compare. As mentioned earlier, I've heard many writers state "I've tried to write a story like... but it just didn't work". I cannot speak for everyone else but I've developed a certain disdain for stories written with great similarity to other stories. The beauty of writing fiction is that there are no rules. Your experience, your voice, your sound, and style are all things that are yearned for from a reader. I want to hear what you have to offer in your fictitious piece. I want to envision myself as one of your characters and avoid doing my dishes from the night before by getting lost in your story! Think about it, did J. K. Rowling become the famous author she is by basing Harry Potter on another fictitious piece? Nope! J. K. Rowling is famous for her creative individuality which separates her story from many other authors of the world -- her own imagination!
Remember that writing a fiction story is reliant on you and your own imagination. There are no set rules telling you what you can and cannot write about -- It's all about the readers you wish to attract and you. Exercising your creativity on any topic that comes to mind will increase your imagination to give your readers a story they would like to hear from you! Remember that another story or concept written by another author is unique to their readers and will not be interesting to that of your own. If so, I'm sure they're already active readers of that author's work. Use every source of inspiration you can get -- yes, you may even rely on nature calls-- and use your imagination to write. We're all very eager to hear from you!