A buddy of mine was recently having issues with the Inner Critic. The beast has hunted writers throughout history. I've heard various bits of advice in handling this creature--writing letters to the Critic (Heckler, as my friend Deb calls him/her), writing fast (outpace him/her), etc.
But, in the end, how a writer handles this demon is as individual as the writer.
I figured out how to handle him for me. In the interest of being helpful to my fellows, here is what I do--
First! I had to figure out how I was being criticized. Turns out it was the "You're no good and never will be" attack. (And this is the most common attack from my understanding...though there's also the "You're too old to be trying this, You haven't learned enough to do this, or You aren't smart enough to pull this off")
The big, telling word, for me, was "You." The critic attacks You, not your work. It seems like it's attacking your work. But it's really going after You.
You must get out of the line of fire.
So my solution was to aim for other people. I write scenes, stories, poems, etc. and direct them to people that I know. I doubt that my targets would recognize themselves very easily (though things like occupations and names sometimes pop up and it's not that hard). If something a friend or loved one said or did inspires me, I put it in. I have my target person clear in my head.
It's important that I think of the stories/scenes as love letters too. The Inner Critic is a negative bastard. I write to people I love and admire--and miss. Missing them helps a lot because I feel like I still need to tell them something, whether or not they hear it.
When you're writing to people you love, it's really, really hard for someone to criticize you.
This has been super-effective for me. And it works for big pieces too. One scene of a novel could be directed towards my husband, another towards my mother, and guess what? It could all be the same character. Doesn't matter. When I'm writing in the moment I can switch up who I'm writing to. The end novel could be an extended love letter to one person, or it could be a series of love letters to everyone I know.