The Small Catechism teaches us to end the day with Evening Prayer:

In the evening, when you go to bed, you shall bless yourself with the holy cross and say: In the name of God the Father, Son, and Holy Ghost. Amen.
Then, kneeling or standing, repeat the Creed and the Lord’s Prayer. If you choose, you may, in addition, say this little prayer:
I thank Thee, my Heavenly Father, through Jesus Christ, Thy dear Son, that Thou hast graciously kept me this day, and I pray Thee to forgive me all my sins, where I have done wrong, and graciously keep me this night. For into Thy hands I commend myself, my body and soul, and all things. Let Thy holy angel be with me, that the wicked foe may have no power over me. Amen.

Then go to sleep promptly and cheerfully.