Sometimes it comes from a song I've heard, a character I enjoy from a book or TV show and my wondering what would happen if they took a different path, or a photo I've seen (we'll talk about my short story "The Pink House" soon). Sometimes, though not with exceptional frequency, it's a news article.
Like this one.
Click on the link to read the article that inspired my play I Am Acquainted with the Night. Details coming soon about that; for now, here's the article: https://www.pjstar.com/news/20170605/luciano-is-this-spooky-face-harassing-elderly-woman