הלכות תשובה ב, א-ד

(1) [Who has reached] complete Teshuvah? A person who confronts the same situation in which he sinned when he has the potential to commit [the sin again], and, nevertheless, abstains and does not commit it because of his Teshuvah alone and not because of fear or a lack of strength.
For example, a person engaged in illicit sexual relations with a woman. Afterwards, they met in privacy, in the same country, while his love for her and physical power still persisted, and nevertheless, he abstained and did not transgress. This is a complete Baal-Teshuvah. This was implied by King Solomon in his statement [Ecclesiastes 12:1] "Remember your Creator in the days of your youth, [before the bad days come and the years draw near when you will say: `I have no desire for them.'"]
If he does not repent until his old age, at a time when he is incapable of doing what he did before, even though this is not a high level of repentance, he is a Baal-Teshuvah.
Even if he transgressed throughout his entire life and repented on the day of his death and died in repentance, all his sins are forgiven as [Ecclesiastes, op. cit.:2] continues: "Before the sun, the light, the moon, or the stars are darkened and the clouds return after the rain..." - This refers to the day of death. Thus, we can infer that if one remembers his Creator and repents before he dies, he is forgiven.

(2) What constitutes Teshuvah? That a sinner should abandon his sins and remove them from his thoughts, resolving in his heart, never to commit them again as [Isaiah 55:7] states "May the wicked abandon his ways...." Similarly, he must regret the past as [Jeremiah 31:18] states: "After I returned, I regretted."
[He must reach the level where] He who knows the hidden will testify concerning him that he will never return to this sin again as [Hoshea 14:4] states: "We will no longer say to the work of our hands: `You are our gods.'"
He must verbally confess and state these matters which he resolved in his heart.

(3) Anyone who verbalizes his confession without resolving in his heart to abandon [sin] can be compared to [a person] who immerses himself [in a mikvah] while [holding the carcass of] a lizard in his hand. His immersion will not be of avail until he casts away the carcass.
This principle is implied by the statement, [Proverbs 28:13], "He who confesses and forsakes [his sins] will be treated with mercy."
It is necessary to mention particularly one's sins as evidenced by [Moses' confession, Exodus 32:31]: "I appeal to You. The people have committed a terrible sin by making a golden idol."

(4) Among the paths of repentance is for the penitent to
a) constantly call out before God, crying and entreating;
b) to perform charity according to his potential;
c) to separate himself far from the object of his sin;
d) to change his name, as if to say "I am a different person and not the same one who sinned;"
e) to change his behavior in its entirety to the good and the path of righteousness; and f) to travel in exile from his home. Exile atones for sin because it causes a person to be submissive, humble, and meek of spirit.