My last agent gave me a piece of advice that I thought was absolutely perfect, and it rang so true for me that I thought I would share. This isn't necessarily going to apply for everyone out there, but on the off chance... He told me that I didn't need to write the "biography of the story." In order to explain what that means, let me describe the way I tend to generate a first draft. (And to be clear, we're talking about long-form works here - screenplays, novels, etc. This isn't as much of an issue with short stories). I usually begin with the seed of the idea, or the hook: the thing that makes me feel like the story might be interesting enough to spend roughly a billion hours working on it and thinking about it. If the hook is good, I start having ideas a mile a minute about how to turn the hook into a story - they usually pop into my head from all parts of the story's timeline. If I have enough, I write them down in a Moleskine notebook (LOVE THOSE) I keep for the purpose, or type them up in a very rough outline format.
Next step is to make a fairly complete synopsis. This, if done right, should read as an extremely abridged version of the story itself. I often include bits of dialogue, and most of the big story beats will be present. There's always room for movement, though - I sometimes shorthand parts (a la "NEO & AGENT SMITH FIGHT" in the Matrix scripts), either because I don't know what I want yet, or occasionally when I want to leave some room for a collaborator to do their own thing (this happens with comic work quite a bit, especially in the fight scenes).
The synopsis is often what I hand to my core group of readers - friends, family and other writers who are willing to check out my stuff in rough format to provide comments. Every writer I know who gets anywhere has their own set of critical first responders. In my opinion, it's essential to find a group of people who will read your work and give you actual criticism (not just an emotionally-tinged whitewash, tantamount to your mom liking every piece of art you brought home from preschool).
Anyway, once the synopsis is squared away, I'll start a first draft. And here's where the problems can start for me. I have a tendency to set up my snyopses like Rube Goldberg devices. Plot occurrence A sets up character moment B sets up payoff C sets up new plot occurrence D. Every event that happens to my characters within my story's timeline tends to show up in the synopsis. That's what my agent meant when he mentioned the "biography of the story." Readers don't necessarily need A-B-C-D. They're sophisticated enough that just A-C might work, and then we could skip to K, and maybe hit B in a flashback or an oblique reference. The unfortunate thing for me is that I don't always see the structural possibilities outside A-B-C-D until I'm well into a full first draft, or even finished with it. I think it's just the way I do things. I need to build the whole skyscraper before I can see what floors are actually worth visiting.
I'm trying hard to get better at cutting before I write, but it's not always a snap. As I think I've mentioned here, I'm writing the first draft of the script for Strongman 2 in longhand, in a lovely Moleskine (LOVE THEM) I carry around with me everywhere these days. I was about 60 pages in when I realized that I was taking way too long to get to the meat of the story, and I could cut almost all of the New York City-set prologue I had originally written. That's better than realizing it after I was finished, or worse, not realizing it at all, but I was able to cut almost 15% out of the planned length of the book with just that one change, and I think the book is much stronger for it.
So, if anyone were ever to ask, yes, I could explain exactly what Tigre and Bujo were up to in New York City before they embark upon their trip back to Mexico in Strongman 2. It's my job to know that sort of thing - it's part of the biography of the story I'm telling, after all. But unless I decide to include it as a deleted scene in the back of the book, I'll be the only person who ever knows.