I used to be extremely self-critical, too, and I'm sure I still am to a certain degree. I have been working on it for years. For me, it comes down to figuring out what messages are being replayed in my head that I am not consciously aware of, i.e. the messages I received from my critical mother, the lies I believe because I am a perfectionist, etc. Once I isolate one, I work on it.
About 10 years ago, I was having a hard time buying my mother a Mother's Day card and suddenly realized it was because we didn't really have a good relationship. The more I thought about it over a few days or a week's time, memories came flooding back to me of how my mother verbally abused me and stripped me of my personhood. I went to the library and got some books that talked about healing from anger issues. Facing Shame by Fossum and Mason was an excellent help at that time. I went through the books, took notes, journaled about my memories and feelings, cried about it, and then one night, as I was crying and praying, I felt an actual emotional transaction in my soul. I was "divorced" from my mother. Sorry. That's the best way to describe it. I had come to the realization that my mother was not the kind of person whose good opinion I really needed to earn anyway, since she and I are so diametrically opposed on so many issues. That day, a great change in me occurred, and even though I didn't tell my husband about it, he automatically could tell I was different. It was a major turning point in my life. The damage my mother did was very great and I had another significant breakthrough less than a year ago.
As I heal from the hurts in my heart, I am able to better accept myself the way I am. I can laugh at myself and not take myself so seriously all the time. I'm a lot happier.
Anyway, that's how I do it. I wish you good success.