I've always been in a love/hate relationship with my body, as I've been overweight for a large chunk of my life (still am, albeit working on it very slowly). It's a hell of a cycle to be stuck in: you're disgruntled with your body, but you have to love yourself to get that extra oomph you need to get it to where you want it to be. So I've taken baby steps, not only in how I approach my own body, but others as well.
For those of us here in America (I'm not sure if those of you in other countries have experienced this), there's a popular saying that I see floating around in the fat positive circles, "Real woman have curves". I used to repeat this to myself, in my head, like a mantra. On top of that, I've been guilty of looking at someone on the thinner side and thinking "Yeesh, someone could afford to eat a little more". From what I've seen, it's more socially acceptable to voice that very same thought, out loud, to a complete stranger, than it is to tell someone fat that they really, really shouldn't eat that.
I've learned, thankfully, that this sort of attitude did me absolutely no good in dealing with my own body image, and the only thing it ever accomplished was to reinforce the idea that an x body is better than a y body, whatever they might be. I absolutely believe that being more compassionate about someone else's body has made me more compassionate about my own, and I've certainly made healthier decisions for myself since I tuned out that little critic in my head.
It's a work in progress, and I have a feeling it always will be.