When I started my potter fic many years ago, I did make some notes, etc, including “behind the scenes” shorts to the other side. Now that I’ve decided to restart that story, fifteen years later, I’ve been finding those notes useful, invaluable actually, in restarting it with some consistency. Overall, if it’s important to the story, or good backstory, I do write it down, either on paper, or in the computer. I even have a database for my original works. Another invaluable file I have, from years ago, is a spreadsheet for the potter story. Given its size, I had columns for each of the major/significant charactors, a row per day of the story, and for those interesting days, a thing or two about what was happening – useful, very useful, to refer to. (And, now that I’m revising, I’ve got some of the older drafts too.)
As to writing the story itself, words definitely flow more easily at a keyboard, especially if I’ve got “inspirational pictures” up onthe rest of the computer monitor. Now, I don’t start with a comprehensive story outline….NO! I will write any key scenes, have a rough idea, and refine it as I write. So, this next section to the current chapter I’m working on, yesterday, I came up with a few points to write to, so I give one sentence snippets, and I’ll likely write to those goals as I work tonight/tomorrow at it. Any “later” ideas that I don’t have a spot yet, will loiter as one-liners in the rough order I intend, until I reach them.