I've never written a book with an outline or a predetermined theme. It's only in retrospect that themes or subjects become identifiable. That's the fun of it: discovering what's next. I'm often surprised by plot developments I would not have dreamed of starting out, but that, in the course of the writing, come to seem inevitable.
The way that I write novels in particular is I don't usually outline; I just write. Part of the fun is discovering what's happening in the story as I'm going along.
I force myself to outline, but not too closely, so I guess I plot by the seat of my pants? My natural instinct is to dive right in, but I know I'll get stuck. I like to stick with the architect vs. gardener metaphor. I guess I'm a gardener who plants tomatoes. I have the sticks in the ground and let the vines grow along those parameters.
For the novels I wrote before selling anything, I didn't outline much. I had a vague idea of the story.
For me, when I 'discover' a story, there is a feeling of buoyancy and clarity, perhaps similar to early morning out on a prairie highway, when darkness lifts and reveals the outline of farmhouses and copses of trees in the distance.
When I signed onto 'Superman,' editors Matt Idelson and Wil Moss gave me a rough outline that JMS had turned in for the remaining issues of the 'Grounded' arc, which amounted to a couple of sentences for each issue, spelling out in general terms where the issue would take place geographically, specific guest stars, things like that.