Whenever I am “hit” with an idea to my book, story, or anything I immediately write it down in a simple three subject notebook. I call it my “Writer’s Bible” as I refer to it all the time when I am writing. In my writer’s bible, I have all my characters with their backgrounds which lists who is related to who and who knows what which helps me focus and keep track of my story.
I would encourage all writers to do so because if you are reading a story and the author/writer contradicts a previously known fact it breaks up the story. The reader would be like, “I thought…wait a minute…” They will then turn the pages back or scroll back to verify their notion. This causes a break in your story flow, and most likely irritate the reader if their conclusion is true.
I carry my journal almost everywhere. I could type it on my iPad; however, writing it with a pen and paper feels like I am doing something, and I get that “writer’s” mentality. You never know when an inspiration will hit you. Could be right before you fall asleep or while you are brushing your teeth.
If you are working on multiple stories or books I would keep separate notebooks or writing journals as you never know how much you will fill.