Good karma means what is prescribed in the Vedas. Specifically, it is prescribed that one should perform yajna. Yajna means actions for the satisfaction of Lord Visnu, the Supreme Personality of Godhead. So good karma means performance of the yajnas as they are prescribed in the Vedic literatures. And the purpose of this yajna is to satisfy the Supreme Lord. A good, law-abiding citizen is one whose actions satisfy the government. So, good karma is to satisfy Lord Visnu, the Supreme Lord. Unfortunately, modern civilization does not know what the Supreme Personality of Godhead is, what to speak of satisfying Him people do not know. They are simply busy with material activities. Therefore all of them are performing only bad karma and therefore suffering.
Lecture on Bhagavad-Gita 16.11-12, Hawaii, 7 February, 1975