Envy is one of the most useless thoughts/emotions there is, it serves no purpose at all.
But there's a good sentence for dealing with it, if you are envious of somebody else having something you can tell yourself: "I have something he doesn't have. I have _enough_."
It is supposed to motivate you to better yourself, sadly most people just use it to explode the envied person's head in their immagination. That, or they join a political ideology well suited for weight-loss.
For me, envy motivates me and defines what is possible. Envy is not an enjoyable motion, but it pushes me out of my comfort zone and to achieve more than I am.
But there's a good sentence for dealing with it, if you are envious of somebody else having something you can tell yourself: "I have something he doesn't have. I have _enough_."