In my "Priorities" post a while ago, I mentioned that I was working on a story that I described as an apocalyptic road trip. Research was done in a couple of weeks, the shortest period of time I've ever had when researching for a story. Even then, the research was focused exclusively on the apocalyptic event (I won't say what that event is; I want to leave some surprises). Another thing that made this research phase unique from others I've gone through is how broad and general it was. With my alien invasion novel, for example, the research was done over three months with an additional two months later, and it was primarily focused on details for the alien invaders: their biology, technology, society, etc. The apocalypse story, on the other hand, left many details up in the air. Like Cormac McCarthy's The Road, it is not important to know the hows and whys of the end of the world. All we need to know is that it's set during the end. We in the audience need to know just enough about how it impacts the lives of the characters.
So research for the apocalypse story took a couple of weeks, a little each night; I probably could have crammed all of it into a single day. Next, I wrote a short summary on the core cast, the survivors that we would travel with. I kept it simple with only ten characters. You never want to bring too many people into a story like this. A multitude of characters can work sometimes, but not in this case, not when one thing you want to stress is isolation. For all their humor and smiles, I'm sure the characters on Gilligan's Island would have killed each other in reality. They just wouldn't be able to stand the same faces over and over again. Keep the characters simple but diverse. Write down a few details about each of them (age, date of birth, place of birth, occupation, physical description), but don't write full biographies. This is an important aspect of organic writing because you want to learn about them as you write, you want to surprise yourself with the details that you discover along the way. If you think through all the details beforehand, the material will seem stagnant. Then, as this is a journey story, you get a road map (I got one of the western United States) and draw out the course that they take. Don't be afraid to let the road wander to and fro, but don't let it wander aimlessly. After all, the characters still need to strive to go from Point A to Point B. A thousand-mile detour to Point C makes no sense. Also, don't expect to follow this path religiously. As you write, unexpected divergences may arise, though I won't pretend to know what they might be. As in real life, you should never predict the future when you do organic writing. You should just try to follow through on the plan you have and take the punches as they come.
Now for the actual writing. I was going to write this story in the third person, no differently than you'd expect to see in a lot of other writing. As I researched, I toyed with the idea of letting one of the characters keep a journal so we can look into the mindset of the survivors of this catastrophe. This is nothing new. We see it in The Road and movies such as Zombieland or Stake Land. With apocalyptic fiction, you want that intimacy. In our everyday lives, we don't struggle through the barren wastelands of a nuclear holocaust, so we have no frame of reference; a survivor relating this experience helps us to overcome this handicap much like when a war veteran talks about this time in combat. This also makes the writing process easier on you. Remember, the key thing we want is surprise. We don't want to know beforehand what's around the corner, and we don't want to know the intimate details of all the characters. Writing in third person, we would need to know about all of the main characters because we would write from each perspective. On the other hand, writing from one character's viewpoint gives us a window to look out through. The narrator doesn't need to be detailed either. Just have a sense of what he or she is like, and allow that person to discover new things about the people around him or her.
There's one more thing about the use of a journal that brings this a little more closer to the organic aspect of this writing. Sitting and writing the story in longhand with little other material lets the subject matter bubble in your mind as you move along. When you write by hand, you have to not think about a deadline because you already write more slowly than you type. In fact, when you write your first draft of an organic piece, I strong recommend that you do it without a deadline in mind. As it takes more time to get your words down on paper, you are able to dwell more on the current situation of the characters. In the rush of typing, you might overlook something and when you need to write the next event, you're stuck and have to think about it. In other words, your mind and your pen are in sync as you write organically.