You all know this but sometimes it needs to be reinforced. Your first draft will be lacking, if not terrible. Easy to get discouraged, move on to another task, or throw in the towel all together after reading it.
However…this is the nature of the game. All the greats (Hemingway to Stephen King) have admitted this. If the titans of this biz have terrible first drafts so will you. Accept it, embrace it, use it to your advantage. Get the first draft written, out of your soul and on to the paper…then you can craft your masterpiece from the foundation you’ve built underneath.
So the answer to the headline question is obvious: just write. Writing is rewriting, this is a basic rule of the trade you’ve chosen, now go fire it up.