When I first got started writing, I'd have an "idea". Since I write mostly SF and Fantasy the idea was usually in the form of some story gimmick: what would it be like to play tennis on the moon? How would an EMT service on the moon work? Suppose psychic powers existed but were really, really limited? Suppose "her world exploded" wasn't a metaphor but literal truth?
And then I'd sit down and start writing, making things up as I went along.
Most of the time the story would fall apart and I'd have nothing. I'd have an opening and either be going in circles or just get stuck and have no idea what to write next.
So I started plotting in advance, outlining the things that happen in the story. I'd still have the stories fall apart in my hands but at least I wouldn't have written a bunch of finished text before reaching that point. And I learned that I can work from an outline. If I ever do collaborative work, that can be important.
So, for a long time then I was a "plotter". But I often didn't adhere closely to the outline. Instead, I'd find the story going in different directions. That was okay. I could just pause, redo the outline to reflect the new direction, and proceed from there. Sometimes it might take several iterations through that before I was done.
But here's the thing. The final stories weren't any more likely to sell when I plotted than when I'd pantsed.
Enter Dwight Swain and his book "Techniques of the Selling Writer".
One of the things Mr. Swain had in his book, on preparing for writing a story, was having a "starting line up." This meant defining five elements of the story: situation, character, goal, opposition, and "disaster". Your character exists in an initial situation. He has a goal he'd like to achieve (which could simply be avoiding some bad thing happening). There's opposition to the character's goal (usually a "villain" of the piece, but not necessarily). And some bad outcome from failure to accomplish the goal, the "disaster".
The stories of mine that failed to get off the ground in the past were usually over the lack of some element in this starting line up. So, lately, I started to spell them out explicitly before starting writing a story. Oh, if I have an idea for a story opening or something I might write that to get a feel for things and then pause to create the starting line up. But I do it, every time.
And the result is that I've found myself going back to pantsing. I can just write the story because the elements I need are there. I can wonder a bit in subplots, explore character a bit, take some time letting minor characters strut their stuff, but with the starting line up to give direction I can keep the story moving in the way it needs to move.
So now my outlines, if used at all, tend to be smaller bits meant to work out particular story problems, a kind of guided free association to figure out how to resolve challenges. (Character is here. I need him there. How do I get him there?)
But that's how I work today. Tomorrow? Who knows. I've changed my working method before and there's no reason to suppose I won't do it again.