Start small. Volunteer your time and talents to a local organization to help people that need help. (we're all pretty experienced in the giving department) - Our part of the country had a flood a few years back, and needed people to fill sandbags and help with debris clean up... stuff like that can be of such great medicine for us with fragile self-esteem.
By helping others, you feel good about yourself.
Set yourself some goals, and tackle them. It's a great feeling, like La Tee Dah said.