Spiritually good karma is one that does not produce any karmic bondage. Good karma does not relate to good actions alone as most good actions result in karmic bondage. Any action, any karma that produces karmic bondage falls under bad karma.
Spirituality demands negation of karma to zero. This is only possible when we indulged in karma nishkama karma way of life. Indulgence in nishkama karma does not produce any karmic bondage. In simple words nishkama karma means indulging in karma with an unattached attitude.
King Janaka (father of Sita in Ramayana) is the best example of one indulging in nishkama karma yoga. Even though indulging in day-to-day routines of kingdom every single day of life, King Janaka never attached self to fruits of karma indulged by him.
King Janaka a Shishya of Sage Yajnavalkya was a self realized soul. He understood intricacies of spiritual life. He succeeded reaching stage of self realization indulging in nishkama karma yoga. For King Janaka it was never good karma or bad karma that mattered, what mattered was never going after fruits of karma indulged by one.
Spiritually also we cannot go after fruits of karma performed as fruits of karma indulged by human beings always belonged to our true inner self, soul atman the spirit existing in heart. The human form was only a medium for soul atman within to cleanse itself of dross impurities within. In field of pure spirituality ego had no role to play. Spirituality demands demolition of ego in totality.
King Janaka succeeded in reaching stage of self realization, God realization only after demolishing his ego in totality. One can practice nishkama karma yoga only after demolition of ego.
Demolition of ego means working like a trustee, a custodian for whom everything all the time belonged to God Almighty. JRD Tata, scion of Tata industry was a Karma Yogi par excellence, one who indulged in nishkama karma yoga every single moment of life.
From day one JRD Tata considered himself, a custodian of Tata Empire, a trustee for whom everything all the time belonged to God Almighty. Never for a single moment in life did JRD Tata ever work for money or wealth alone. The goal of JRD Tata always was welfare of mankind at large. JRD Tata put welfare of clients, workers and entire mankind before gaining wealth for the company.
Spiritual travelers must copy lifestyle of King Janaka or JRD Tata to excel in spiritual life.
God practically had no role to play in karma. Ever since creation of cosmos God Almighty acts as a Dhrishta (onlooker), never interfering with creation of his! Everything in cosmic system is self-propelled dictated by inscrutable laws of karma and evolution. As we indulged, accordingly manifested our destiny! As our indulgence, accordingly the results!
Good karma in non-spiritual parlance can be treated at par with good actions but in field of pure spirituality, even good karma can be bad for spiritual progress. A spiritual traveler must always indulge in karma whether good or bad in a manner that it does not create any karmic bondage.