The following is taken, with a little adaptation from John Knox's liturgy (1560). My thanks to Paul Levy for showing me this:
Almighty God, we are unworthy to come into your presence, because of our many sins. We do not deserve any grace or mercy from you, if you dealt with us as we deserve. We have sinned against you, O Lord, and we have offended you.
And yet, O Lord, as we acknowledge our sins and offenses, so also do we acknowledge you to be a merciful God, a loving and favorable Father, to all who turn to you. And so we humbly ask you, for the sake of Christ your son, to show mercy to us, and forgive us all our offenses. Forgive the sins of our youth, and the sins of our old age.
By your Spirit, O God, take possession of our hearts, so that, not only the actions of our life, but also the words of our mouths, and the smallest thought of our minds, may be guided and governed by you. Through Jesus Christ our Lord, to whom, with you and the Holy Spirit, be all honor and glory, now and forever. Amen.