Have you read "On Writing," by Stephen King? His advice is simple: Pick an hour of the day, plant your butt in a chair, and do nothing but write. You can not write if you want, but you're there for the hour and you can't do anything else.
It's amazing how much the inner editor shuts up when the alternative is paralyzing boredom.
Alternatively, you can go by word count instead. That's what I ended up doing, after I got the designated writing slot down. When you have to make 1000 words a day regardless, your inner editor gets a lot less mouthy.
Reward motivation works too. I don't get videogames until I finish writing, and it turns out my inner editor loves him some videogames.