A blog post recording by Beth Lapides, the "High Priestess of Alternative Comedy" gives some hints as to how you can quiet negative voices and keep on writing (although in her podcast she was actually talking about how to quiet the negative voices when you're onstage doing stand-up comedy). Here is what I gleaned -- you can see how it applies to writing.
- Remind yourself of your motivation for writing the piece -- what was the point in the beginning?
- Engage with the audience -- try to talk directly (in your mind) to the people who will be reading your work
- Re-connect with the core thread of your argument -- write it out to remind yourself if necessary
- Figure out your "take" or point of view -- what is your unique angle?
- Become clear about your "entry point" into the material. Where does your part of the story begin?