The Catholic Sacrament of Reconciliation (also known as Penance, or Penance and Reconciliation) has three elements: conversion, confession and celebration. In it we find God’s unconditional forgiveness; as a result we are called to forgive others.
Act of Contrition Prayer
My God, I am sorry for my sins with all my heart. In choosing to do wrong and failing to do good, I have sinned against you, whom I should love above all things. I firmly intend, with your help, to do penance, to sin no more, and to
avoid whatever leads me to sin. Jesus Christ suffered and died for us. In his name, my God, have mercy. Amen.
Examination of Conscience
Before celebrating the Sacrament of Confession, one should prepare themselves with an examination of conscience. An examination of conscience is a “prayerful self-reflection on our words and deeds in the light of the Gospel to determine how we may have sinned against God” — Glossary, The Catechism of the Catholic Church
There are various types of examinations of conscience but regardless of which one you use to prepare yourself for the Sacrament it should be rooted in Scripture; particularly, the Ten Commandments and Beatitudes. You can view examples here of Examinations of Conscience that can help you prepare for the Sacrament.