Basically I'm writing up the backstory of a world which I will be using as the setting for a particular story/novel, and eventually others in the form of picking and choosing from particular events and times, and elaboration. In other words, setting myself up so that if the first novel succeeds, I'll have no shortage of extra stories.
It's a long and tedious process, though. I'm just winging it so far, jotting down a flow of ideas that I'll later flesh out, edit, cut, change, rewrite, add on to, etc. etc. Until I have this big, huge thingy which will be totally and completely believable as a world. Tolkien-style, except I've got an earlier start than he did.