Your inner editor is the writing equivalent of your conscience. Jeanette Ingold said, "Your internal editor is no-nonsense; wants to keep you out of trouble; and doesn't want you to make a fool of yourself."
In cognitive science terms, your inner editor is a left-brain entity that, like its kin, focuses on detail. So a common thread in all the particular techniques is to give your inner editor a detail-oriented task to keep it busy (the mental equivalent of giving a child a coloring book). This is why drives, or long showers are often settings for inspiration: the left-brain busies itself with the details of keeping the car on the road or registering the white noise of the shower, freeing the right-brain to make associations.
So what specifically can you do as writer to quiet your inner editor? I have a number of suggestions in a longer discussion on my blog, but here are two that I've found particularly helpful.
First, be somewhat systematic about your writing. If you work to a regular schedule it's easier for your left brain to believe it when you tell it that you'll come back and correct the details errors during a future writing session.
Second, enlist your inner editor with detail-oriented tasks that support your writing. Your inner editor loves to make calendars or time-lines of key events in your story, character bios, outlines, and any sort of list. All of these artifacts help address your inner editor's fear that you get key details wrong.
Of course, it's easy to fall into the trap of appeasing your inner editor so much that you don't get any actual writing done (e.g., what fantasy authors call, "world-building disease"). The key is to time-box your inner editor: I often start a writing session with ten or fifteen minutes of detail work to both quiet my inner editor and to warm up.
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