When researching writer Joshua Ferris for my class discussion of the hilarious office novel Then We Came to the End, I came across this interesting interview that offered good advice about writing backstory for characters:
Dave: A massive cast, characters flitting in and out of the frame. It's still early in your book when the chair swapping gets out of hand; readers aren't yet so familiar with all of the characters. Marcia hasn't entirely become Marcia, if you know what I mean.
Ferris: One breakthrough for me, in terms of the writing, was that I ditched backstory prior to starting the action.
I had a key of sorts for the characters. When something would happen or description would apply to someone, I started off by looking at the key and filling it in, determining who these characters were by the accretion of details.
In the beginning, the characters were as new to me as they were to the reader. I became more familiar with them as I went along.
Dave: How much did you backfill? Once you'd reached the end, did you go back and edit significantly, or did the material come out close to finished the first time?
Ferris: Ninety-nine percent of it was done by the time that I reached the end.
I had spent a long time trying to figure out how to work the first person plural — and screwing up repeatedly. I spent probably two years in a state of constant anxiety about it. I set it aside and sort of thought, This is the book I tried to cut my teeth on. It'll never see the light of day.
Then about a year and a half later I got the voice. I got the first two or three sentences in my head, and I just knew that I could write it. I knew how to balance the we so it wasn't always just griping about work; it was balanced with what is enjoyable and meaningful about work. I knew then that I could do it.
Because I had spent those two years failing at it, I knew the story very well. I knew that someone had a daughter that had been abducted. I knew somebody was always bullied for being the middle manager. I knew a central boss character might or might not have cancer.
Once I had the voice in my head, it became a very easy back and forth — I would write on the book for as long as the voice was entertaining, and when the voice got long in the tooth I would switch to the plot and specific events. I just carried that through. Because I had done all that preparatory work, I wrote the book in about fourteen weeks. It was very fast.
Read the rest of the interview here: http://www.powells.com/authors/joshuaferris.html