Heinlein’s index cards
I keep with me at all times 3 x 5 file cards on which I make notes—at my bedside, in my bath, at my dining table, at my desk, and everywhere, and I invariably have them on my person whenever I am away from home, whether for fifteen minutes or six months. An idea for a story is jotted down on such a card and presently is filed under an appropriate category, in my desk. When enough notes have accumulated around an idea to cause me to think of it as an emergent story, I pull those cards out of category files, assign a working title, and give it a file separator with the working title written on the index. Thereafter, new notes are added to the bundle as they occur to me. At the present time I am filing notes under sixteen categories and under fifty-three working titles.
A story may remain germinating for days only, or for years—two of my current working titles are more than twenty years old. But once I start to write a story the first draft usually is completed in a fairly short time. Thereafter I spend time as necessary in cutting, revising, and polishing. Then the opus is smooth-typed and sent to market.