I also measure my self worth by what I do for others. Usually it's the little things, I smile at everyone, I compliment people whenever I can, I donate blood, those are the things that make me feel I am "good". However, I also have doubts as to whether what I am doing is what "God" wants me to do. I am uncertain what comes after this life, so there is always a certain fear, if you will, about my path. Also, I recognize that I am imperfect, and have faults and make mistakes, and sometimes wonder if those mistakes are going to cost me the good part of the hereafter.
While I am uncertain, I do my best, and I think about how to better myself, and that, I believe, is a good way to become a good person.