Repentance is a precondition for God's favor (2 Chron.7:14).  Jesus preached, "Repent, for the Kingdom of God is at hand!" (Matt: 4:17)  This prepares us for receiving the kingdom of God in our hearts.  Repent from what?  From Idolatry and Disobedience, individually and corporately.

Lev.26:40-42 says, "If they will confess their sins and the sins of their fathers ... then when their uncircumcised hearts are humbled and they pay for their sin, I will remember my covenant ...."  1 John 1:9 says, "If we confess our sins, God is faithful and just and will forgive us our sins and cleanse us from all unrighteousness."  The Old Testament points out that confession must be followed by repentance and perhaps restitution.

One of the preconditions for bearing the Fruit of the Spirit is repentance (Galatians 5:24).  For the new Christian nature to grow, the old Adamic nature must be 'put to death' by repentance (Colossians 3:5-11).

It is best if you have one other Christian you can use as a confessor, perhaps be co-confessors.  James 5:16 says, "Confess your sins one to another and pray for each other that you may be healed."

Here's a repentance sheet that breaks the power of sin.

Here's a checklist of sins and traumas that you can use as a reminder.

Here's a checklist of idolatry and occult behavior you can use as a reminder.

(P.S., this is called "sanctification.")