I figured I'd go and explain how I create a story. Maybe it'll provide a good reference point to someone, who knows.
So here's how I(as an individual) plan out my writing process: I have a single idea, maybe it's about a fantasy world where flying fish alien invaders are coming from the sky. I usually go with a fairly fresh concept, or at least something interesting. Then I build the story from there while using the aforementioned "why" technique.
Why are the flying fish aliens invading? They're aliens, so what is their technology level? Is this a low technology level fantasy story or is the story going to be about technology vs. magic? What special traits do these fish people have that makes their brand of "alienship" different?
I also have to build the world:
What kind of world are these aliens trying to invade? What is its technology level and how are the nations reacting to the alien invasion? Will a monarchy's reaction be different from that of an empire? What about any democratic, or even entirely scholastic societies? What will be each nation's main weapon/tactic of choice? Will they unite to fight this threat, or will they stand divided?
Finally, I focus on the story: Who are the main characters? How do they fit into the world? What is their role is this conflict? Why should the reader care about their struggle: for example, is this a simple story about a family dad trying to provide for his family in a destroyed world, or will the family dad eventually become the head of a small group, growing his influence and stature as he becomes the "dad" of a bigger family. Will he eventually become a key player in the war against the flying fish aliens? What is the supporting cast like, and how do their motivations CLASH with the main character? Will they be reconciled with him/her and will they accept the main character's ideals, or will they eventually resort to undermining him, maybe even betraying him?
Once the big questions have been answered, it is(for me) usually easier to plan out the plot. I recommend adding a few twists here and there so that the story doesn't become too predictable, and some twists can turn the entire story up on its head(like "the space aliens were the good guys the whole time" ...please be careful with that particular trope if you plan on using it).
I hope this is of use to someone.
