What has been a bit helpful for me was to create a "dream board" with positive happy images and phrases. I chose pictures from magazines of people doing things I hope to do (dancing, playing with my kids, watching them play with each other, yoga, snorkeling etc.) and some of the phrases I chose were "I love my body now", "Your tougher than you think", "Every day is an opportunity", and "imagine choosing your own path to wellness.
I framed this even though there are still some white spaces I continue to add to it when something I see is inspiring and moves me. It is right by my bed so I see it first thing in the morning and last thing at night.
My therapist (Who I just recently started seeing) told me to tell myself something good about myself when I wake up (like I am strong, I am funny, I am worth it whatever) and also when I have the negative thoughts run through my mind to launch a counter attack even if I don't believe it.
So this has helped me, I am happier and the thoughts come less frequently. Also writing them down gives me some release too.