I've written the first chapter (all first drafts) and now I'm all over the place with it. My big thing is what happens in between the main events. I'm starting to feel like I've never read a novel in my life.
Thats how I feel! As though I've no point of reference to follow as I try to put words together.
When I do NaNoWriMo (national novel writing months 50K word challenge), it's always a huge help. They encourage you to write, write, write without your internal editor. I mean, no editing, no re-reading, just hardcore cranking out of words. It's pretty crazy.
But it does help- you start to see where your story has to go, and you get a lot of practice. So, I guess my advice to you (as though I'm some sort of expert? I'm not...not in the least) is to just go for it right now and put down as much as you can even if it's not pretty. That can all be done later. (and THATS the part I'm can't help you with, since, I can't seem to get that part right myself)