12th Street is running a series on this. I contributed an equation, which tracks who one's audience is through the drafting process:
"Audience Equations for Myself (and/or anyone who is interested (in terms of a something intended for publication))."
Draft 0: Taking notes, not sure what it is, experimenting, etc.
Audience = self. (No rules, no boundaries, no structure, no worries. Not all projects have this draft; if you can, begin at “draft 1″)
Draft 1: A draft is defined as a whole unto itself: it can be read through and it more or less makes sense; a writer usually gets about five of these before the project loses focus.