I mean that depends on what ethical framework you apply. Like you could give a tautological answer like good is who does (mostly) good, but that just moves the question to what is "good".
And there are apparently a number of possible contestants:
Virtue ethics : What is moral is what makes us the best person we could be.
Deontology : What is moral is what follows from absolute moral duties.
Utilitarianism : What is morally right is what generates the best outcome for the largest number of people.
Rights-based Ethics : What is moral is that which is in accord with everyone's rights.
Care-based Ethics : What is moral is that which promotes healthy relationships and the well-being of individuals and their interdependence.
And there may be even more than that. And as you can see depending on what you describe as good or moral, has different implications on how you should act. Some are concerned with what you do, others with the result of your action, others with rules and rights, others with a functioning society. And as a consequence at least some of them can produce situations which are mutually exclusive with the rest.
So it's pretty much impossible to answer this question in a general straight forward way. As Mr. White in the comments mentioned it's probably easier to define good via it's antonym bad. Because it's often easier to say what doesn't work than what works. But that again has the problem that you can only argue after the fact what was good or bad.