Most writers work in two distinct modes:
Creative mode: In creative mode, you give yourself the freedom to try different things, with the understanding that they may work and they may not. Writing badly in creative mode is okay. Everyone expects that a lot of what you write in creative mode will be bad (and of course, some will be good). Creation is anarchy, so get a little crazy when you’re being creative. That’s what you’re supposed to do.
Editing mode: In editing mode, your goal is to clean up the mess that you made in creative mode. You analyze what you wrote, you recognize the good stuff, you throw away the bad stuff, and you straighten it all out so it makes good sense.
Writer’s block is what happens when a writer tries to write in both creative mode and editing mode at the same time. Don’t do that! It’s like driving with your foot on the gas and the brakes at the same time. Creating a little and then editing a little is okay — just don’t edit it before you’ve actually written the words! As the old saying goes, get it written; then get it right.
You always write your first draft in creative mode. When we talk about a first draft, we mean the first version you write on the page or type on the screen. Everything after that is edited copy. If you’re doing your job right, some of your first draft will be excellent, and some will be awful. Your goal is to make sure that all of your final draft is excellent, and the only way to get there is to start with a first draft, no matter how bad.
Give yourself permission to be bad on the first draft. After all, your editor isn’t going to see that first draft. Just get it written. Later on, when you go into editing mode, you can worry about making it pretty. After you finish editing, everyone will think that you were brilliant all along. Only you’ll know the truth, and you don’t have to tell anyone.
On a blank piece of paper, write out this sentence: “I have full permission to write a really bad first draft, because I know that most first drafts by most authors are mostly lame. I’ll get it right on the revision.” Put today’s date at the top and your signature at the bottom and post it over your workspace.
Quoted from: Writing Fiction for Dummies by Randy Ingermanson