There are multiple ways to write. A few examples: a) you already have the story in your head, pretty much in its entirety (this happens to me sometimes); b) you invent a character, put it somewhere, like a store or a cafe or a gym, and let the character take charge of the story; c) and I just thought of this one, you can discuss a topic that interests you with a friend while recording the conversation. Then listen to it and transcribe your more interesting remarks.
I suppose that last one would be better suited for essay writing.
There’s a documentary on Kenneth Koch on YouTube, and he mentions a technique whereby he just gets behind a typewriter then writes unfiltered. The he goes back and edits — or more like, salvages.
I also read an interview in the book The Essential Allen Ginsberg where Ginsberg advised his writer friends to do like he does if they want to put out a book: go though your journals and pick/choose/edit.