To add to this, I recommend you take a look at a very interesting and well-written book by Daniel J. Levitin called The Organized Mind: Thinking Straight in the Age of Information Overload. Among many other things, Levitin breaks down the index card technique and advances the reasons that successful creative people use this method of organizing their lives or, for our purposes, how writers come up with their stories. What he presents reads like a textbook for how to invent the plot for your story idea.
The main point Levitin makes on this topic, having interviewed in-depth hundreds of successful people, is that we need to externalize our thoughts and bits of information that our brains are constantly manufacturing in order to free the creative side of our head and make room for new fresh thoughts to emerge. He states, "People at the top of their professions, in particular those known for their creativity and effectiveness, use systems of attention and memory external to their brain as much as they can. And a surprising number of them, even in high-tech jobs, use decidedly low-tech solutions for keeping on top of things."
He goes on to recommend using the index card approach to capturing bits of thought and ideas:
"Imagine carrying a stack of 3 x 5 cards with you wherever you go. When you get an idea for something you're working on, you put it on one card...Every time any thought intrudes on what you're doing, you write it down... The rule is one idea or task per card--this ensures that you can easily find it and dispose of it when it's been dealt with. One piece of information per card allows for rapid sorting and resorting, and it provides random access, meaning that you can access any idea on its own, take it out of the stack without dislocating another idea, and put it adjacent in the stack to similar ideas. Over time, your idea of what is similar or what binds different ideas together may change, and this system--because it is random and not sequential--allows for that flexibility."
The point of all this, of course, is that Levitin is describing how a writer can best invent both the major movements and the nuances of his or her developing plot. The book is fascinating in explaining in some detail how our brains work and, for a writer, it starts to make some sense of the mystery of how we can manage to create something intricate and significant out of nothing.
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I'm the Program Director of the low-residency MFA in Writing for Stage and Screen being offered by the New Hampshire Institute of Art. Our next residency runs January 3-11, 2016 and we are now considering applications for starting the program in January. I'm also a playwright and screenwriter, producing partner in my production company Either/Or Films (The Sensation of Sight and Only Daughter), and a professional script consultant.