Therapy helped me a lot.

I've had to learn to notice when I'm mentally putting myself down and then turn those thoughts around.

I had to figure out what abusive messages I was carrying around inside, especially from my childhood. I had to (and still sometimes have to) then realize that they weren't true, and then even figure out what was and is true.

One technique that often helps me is to pretend that a good friend is going through what I'm going through, what would I tell them? How would I advise them?