The rabbis are also very clear on another point: It is essential to ask forgiveness from a person you have wronged before asking for God's forgiveness. You must also do everything you can to make the person whole. If you've committed a murder, this puts you in a difficult spot. So remember that. This is also the time of year when you are expected to pay your debts.
The Jewish liturgy is pretty savvy about human nature. The rabbis must have known that lots of us, faced with the necessity to repent, will say, "Gee, I've had a pretty good year. Haven't committed any sins I can think of." Perhaps that's why we do confession as a community, not individually.
In a prayer called the Al Cheyt, the sins are itemized. Here are some samples: "For the sin we have committed against you by evil speech . . . by wanton glances . . . by hardening our hearts . . . by envy . . . by desecrating your name . . . by effrontery . . . by tale bearing . . . by causeless hatred . . . by perverting justice." All bases are covered by confessions of sinning "knowingly and unknowingly," and "intentionally and unintentionally." If you cannot find yourself on that list, then you obviously need to look harder.
Psalm 130 captures the spirit succinctly: "Out of the depths I call to Thee, O Lord. O Lord, hear my voice; let thy ears be attentive to my supplicating voice. If thou, O Lord, shouldst keep strict account of iniquities, O Lord, who could live on? But with thee there is forgiveness . . . "
This kind of humility is a healthy antidote to the narcissism of modern life.