Be objective and open minded. Although you think something is wrong, another person may see it very differently.
Allow them to have their opinion and only then do you have a right to have your own. Assume your opinion is wrong, and you may learn something new because your mind will be truly open.
Exercises
Experience the Poor Side of Town
Spend half an hour or so walking through the streets of a very impoverished neighbourhood or shopping area. Look at the people to see what you could be if not for your good luck and effort.
This exercise, done daily, will bring home the value of the lucky life you have. It will help overcome self-pity and help you appreciate everything.