How do you fight negative self-talk?

Inspired by janbb’s question.

When you find yourself about to criticize yourself, or beat up on yourself, to excess or to no good purpose, what do you do to fight it? Did you learn these things from a friend, a therapist, or just come to them on your own?

I grew up in an abusive household and now that I am out of it, I am my own worst enemy. I’m getting better at it, but I still do this far too often.