This is critical. Your first draft is going to suck, and hardcore. Just accept this fact and writing will be much easier. Don't edit, don't correct spelling—just write, full stop, and get your ideas on paper. You'll find this tip frees you; it will allow a deeper connection to (if you'll indulge me) your "muse." When you finish the first draft, walk away from it. For a day if you can, at least a couple of hours if you can't. When you come back to it, you can look at it with a more critical eye and you'll find some obvious edits that need to happen.