Give yourself permission to write a shitty first draft. The main goal of the first draft is simply to get everything in your brain on paper; it doesn't have to be perfect.

Then take a week off, rest, and only then go back read what you wrote, then start polishing, rewriting, and revising.

And realize it's going to take a long time. My first novel (see the link in my sig) took six years from first draft through the seven drafts it took before it was ready to go to print.