How do I stop being selfish and actually start taking interest in others?

I feel at a crossroads. I used to be such a pessimist and a narcissist; I pretty much only cared about myself and kept to myself. I didn't ever keep up to date with world events, snubbed people all the time, never got close to anyone...And now, I feel compelled to give people a chance. I want to become actively involved in bettering the quality of human life somehow, maybe by volunteering or getting involved with local movements. But at the same time, I don't have faith in people and fear that they will just hurt me all over again, that the human race is hopeless, so why bother? I actually distrust people that LIKE people, that are active politically or socially because I wonder what they see in their fellow human beings...But at the same time, I want to help too, I want to have friends...How do I let go of my old mindset that people just aren't worth it?