For school, I usually did outline. But, for fiction, I usually worked differently.
Originally, I would ponder an idea for a while, then sit down and write it. Usually the writing was more a means of pinning down the revolving wheel of possibilities of a plot or scene than anything else. Did this happen or that happen? Did it happen this way? Or a different way?
Now the stories are getting longer and more complex...And there's so many of them running through my head that I have to get organized.
When an idea pops into my head that I think will make a good story, I ponder it a bit. Then I sit down and write out some story notes. This is especially important when I don't have time to work on the idea right away.
Story notes include: Main characters. Original characters get more description and definition. Canon characters from a fandom less so. Details: Physical characteristics, personality, pertinent background information, and of course, why is the character there? Enemy? Love interest? Protaganist?
I usually include the "hook" -- that would be the interesting event or situation that starts the story. A fight, and abduction, a discovery...whatever. Often this is the initial conflict...By definition a story must have some sort of conflict.
I also include a synopsis of the plot, at least as far as I've been able to think it out at the time I jot down my notes.
I include any special scenes I've already envisioned, hopefully in the context of the plot. Love scenes, fight scenes, important conversations or revelations, etc.
If any particularly good lines of dialog have occurred to me, they go in there too.
Any other info I think I might need will probably get chucked in there too. For instance, if it is a song fic, or inspired by a song, I might include the lyrics.
All this is written solely for my own benefit, as no one else is ever intended to read these notes. They don't have to be pretty or well worded. The point is to get enough down that I will be able to pick up my train of thought later when I'm ready to write. And once I start, I can go back to my notes to see if I'm heading too far off base.
My notes might be anywhere from a paragraph to three pages, depending on the complexity of the story and how much pondering I've done.
'Nuff said.