Here is a fantastic prayer I pray before going to sleep. It has many times protected me when I was molested my nightmares. It's especially good for young men.
Now that we are about to lie down to sleep, grant us, O Master, the repose of our soul and body. Preserve us from the dark slumber of sin, and against any impure satisfaction that roams about in the darkness of night. Quiet the assaults of our passions, arrest the darts that the evil one insidiously throws at us, still the commotions of our flesh, and calm all earthly and worldly feelings within us. Grant us, O Lord, a watchful mind, innocent heart, sober hearts, a gentle sleep free from evil dreams. At the hour of prayer arouse us, strong in the practice of your commands and ever mindful of your desires. Grant us the grace to sing your glory throughout the night, to praise, bless, and glorify your all-honorable and magnificent name of the Father, Son, and Holy Spirit, now and always and forever and ever. Amen.
It's written for monks but adapt it as you see fit. (Monks use to get up around 3am and pray the Office of Prime, that's what "the hour of prayer" refers to, though certainly it can apply to Lauds as well.)
This is an example of a pre-written prayer I really like. It's a Byzantine prayer.
