There is a lot to be said about rigorous planning and writing everything down so that when you go to write all of your notes are there. But you could make a case for writing what comes to mind in the moment. A lot of the early work I did was like that and I don’t think I even thought to note things down or keep my ideas somewhere other than in my head for several years.
This isn’t to say there’s a right or wrong way to do this or that one of these methods is what the “real” writers use. There’s just two sides to everything. What I can tell you is that even if I don’t look back at the notes, the things I write down for later are much less likely to be forgotten by me before I can use them. And that used to be a big problem. I would come up with brilliant ideas and spend hours trying to remember what I had thought of.
I keep pretty meticulous notes now; I recently bought a leather cover for a note book that has pockets and pouches and all manner of other little storage areas. But most importantly it’s able to be moved from notebook to the next (because they will fill up).
Sometimes the act of simply brainstorming and putting words or phrases down on paper is enough to generate new ideas and help you through a rut you’ve fallen into. They’re also easily portable and a good place to keep old ideas that you thought might have been wrong. There’s a lot of room to retry things, especially if you feel you didn’t have the skill or maturity for them before.
There is a trap to fall into with planning notebooks: over-planning. It can be tempting to plan until the finest details—things you won’t even need—are laid out for your writing, but sometimes you have to just pick up what you have and write. I’ve heard the authors over at Writing Excuses describe it as “World Builder Disease”. Seems to be a fitting name.
Right now I am working on two separate things, but the main piece is very much in it’s infancy at this point and I am trying to figure my starting direction. We’ll see how this run goes.