It is a good question! There are very many character traits and normal behavior that define a person as a “good Jew”. A few examples: belief in God, treating one's fellow man favorably and giving charity to the needy.
However, there is a novel idea presented by Rabbi Moshe Teitelbaum1841), the founder of the Satmars negative traits were so deeply ingrained in him that he felt that he could not succeed in changing his lifestyle completely. Until, one day, he met a wise rabbi who told him, "In whatever you do, always be truthful. This will guide you to full righteousness and repentance."
The robber listened to the words of the rabbi. Soon after when he was on the way to break in to someone's home, a stranger passed by and asked him where he was going. His first reflex was to lie, but he remembered the advice given to him by the rabbi. He said, "I'm going to So and So's house to break in and steal something." He found that he was too embarrassed to carry out the robbery. And sure enough, little by little, being truthful helped him to change over for the better.
I think this story helps answer your question. A person who wants to be a "good Jew" should be careful to try to maintain distance from all falsehood.
