Prove your haters wrong
Work hard on the weaknesses people are using to mock you.
For example, if they say you are fat, take serious action to lose weight, not only for them but for your own health. Instead of being bitter, set goals and work towards achieving them.
Ignore opinions from others that are meant to discourage you.
For example, do not yield to people who just think you are unfit to handle a particular business or project. Sometimes, they have the desire to always be better than you and simply wish to tear you down. Prove them wrong, but do so the right way.
Accept the ugly reality that people will always criticize you.
Think about how you can use these criticisms to become better.