Beats me. Let me tell you how the hacks do it.
The Fly's brain doesn't work sequentially. It skips about from idea to idea. Sometimes the ideas don't bother to run in order, either: it means that I'm forever taking dictation (as it were) without being told in which order to put the pages. It's up to me to take time to stop writing new stuff and organize the stuff I already have, to make sure that bits of entirely different stories get properly sorted. Certain ideas have even been taken out of one class (lasers v. non-lasers) and put into the other as I discover that they work better that way.
I also have a file I update and back up regularly, with hunks of many of my stories as best as I remember them. I was forced to start the thing because, after making a list, I have no fewer than 25 stories still in progress.
This is how you, gentle visitors, get a blog post about my supposed creativity instead of something that's actually creative.