I have never looked forwards to a blog post with more anticipation. Here goes.
This is how I approach the topic with multiple drafts - generally with much dancing and skipping around in happiness. This approach may turn some people green, but it is how I do it.
The first time I ever wrote an entire, original novel, I approached writing like this: write what ever comes to your brain, fix it afterwards. This is all very well and good, as long as you don't mind at least 6 total rewrites (I kid you not. And by rewrite I mean starting from page one on a blank sheet of paper).
Another method I have devised, which seems to work better for me involves three stages: Planning, writing, and fixing.
Planning, for me, consists of knowing what happens at the first major turning point, knowing my characters, and that's it. Nothing more - otherwise it just kills the story for me. It must also be noted that I do a lot of "percolating" before hand, where I think about the story and the characters non-stop for about a month. Some would call that planning in the head, but I think that's different. Planning requires structure, and there is no structure to my thoughts. They just... are.
Then I sit down, and write to the first turning point. I know what this turning point is, and I don't worry about the quality of writing to start off with (this is we the other drafts come in later). I don't really worry about world building either - if I have something fantastical/out of the ordinary that I have to describe, and don't know how to, I'll do something like this
(Insert description of slum here).
I do this because I know any attempt to describe it will be crap, unless I take a significant amount of time and put a significant amount of thought into writing it. There isn't place for that in my first drafts - it slows me down, and it makes writing hard.
After I reach the first turning point, I stop, and think about my second turning point and end. By this stage, I know my world and my characters, so I think about where I want both of them to end up. I think about potential conflict between characters. And then I sit down and write. And write, and write, and write. I don't describe anything that's too hard, I do a terrible job of the show don't tell rule, and my writing is generally atrocious.
But that doesn't matter - as long as the character motavations make sense, and the plot keeps going, all is good. (First time I wrote The Manda, I ignored both these things. Thus the 6 total rewrites)
Then comes the fixing : I look through the book, try and make sure I get rid of any plot holes, any character discrepancies. Large chunks, especially the middle, will be re-written. This is the second draft. I still don't bother with the writing all that much.
Now we're into third draft territory. This is where I sit down, realise no-one else is going to be able to understand this, and go through the entire thing slowly, chapter by chapter, filling in all the descriptions I left out, doing all the research necessary.
Then I leave it. And come back to it. This is the fourth draft - it isn't a rewrite like the others, but a revision. I strike out all the descriptions that hold the story back, rewrite the ones that don't work. By this stage, it's about ready for Beta readers.
They will find a heap of problems with it, I'll go and fix it, and the whole thing will start over. By the end of the Beta revision, I am done.
And that, for me, is multi drafting. Each draft has the possibility of extending into multiple versions of itself - for example, I may have three second drafts, each for a major plot hole or character inconsistency.
But for me, multi-drafting presents me with an immense amount of freedom. I can stuff up some stuff while I get the other stuff right. I'm only concentrating on one thing at a time (notice also that I start with the hardest things - plot and character - and work my way down to concise sentence building) It won't work for everyone, but I find it immensely helpful.