Don’t focus on other people’s holiness or lack thereof. Give them the benefit of the doubt. They may be closer to God than you think.
As for yourself, just do the best you can at every stage of life and maturity. The conscience is formed and educated, first by our parents, then by teachers and priests, sometimes by friends (I have a favorite saying: “The best friends bring out the best in each other.”), and also by ourselves.
Take an active role in your own spiritual development. If you put a little effort into it, you can learn quite a lot about right and wrong and how to live in the Christian way by literally attending (as in paying attention to) Mass and by participating in other faith-building opportunities that may be offered in your parish, like Bible study/discussion groups, or catechism study programs like Why Catholic. Look at the Church bulletin or website, or call the office to see what’s available.
If you are good at self-study, try reading one of the many Catechism books that are available: YouCat, the United States Catholic Catechism for Adults, the Compendium of the Catechism of the Catholic Church, or, if you’re feeling brave, the Catechism of the Catholic Church.
Let me quote a few paragraphs from the Catechism of the Catholic Church:
II. The Formation of Conscience
1783 Conscience must be informed and moral judgment enlightened. A well-formed conscience is upright and truthful. It formulates its judgments according to reason, in conformity with the true good willed by the wisdom of the Creator. The education of conscience is indispensable for human beings who are subjected to negative influences and tempted by sin to prefer their own judgment and to reject authoritative teachings.
1784 The education of the conscience is a lifelong task. From the earliest years, it awakens the child to the knowledge and practice of the interior law recognized by conscience. Prudent education teaches virtue; it prevents or cures fear, selfishness and pride, resentment arising from guilt, and feelings of complacency, born of human weakness and faults. The education of the conscience guarantees freedom and engenders peace of heart.
1785 In the formation of conscience the Word of God is the light for our path; we must assimilate it in faith and prayer and put it into practice. We must also examine our conscience before the Lord’s Cross. We are assisted by the gifts of the Holy Spirit, aided by the witness or advice of others and guided by the authoritative teaching of the Church.
And I pray that the Holy Spirit may assist and guide you on your way.