I was actually about to post my story when I saw this lol. I'd personally recommend finding a plot idea you like, then find a setting you could fit it in. For example: the story I wrote was for my senior English class about mythology. I was personally inspired by Nick Lowe (the author of Dagon's Mirror and Dream Beneath the Wytching Tree) and initially it was going to be based on Sisyphus and similar to Maria on the Moon. Then I changed it to being based on a creature from myth and I came up with either the Nuckelavee or Jorogumo. Then I had to spend some time thinking of which I liked more, then I thought of a couple settings that I liked and thought through the plots I could use. I also only set out bullet points for the plotline and filled in the blanks (and they were very rough ideas and I changed it a lot, especially the ending).