So, the most helpful thing is Kriat Shema al Hamita—the Bedtime Prayer.
This can be found in every Orthodox siddur (prayer book). There are different versions of Kriat Shema according to custom, but they’re all highly effective and the differences are relatively minor.
All of them contain a prayer to forgive others, the Baruch Hamapil prayer, the Shema verse, the Baruch Shem Kavod verse, and the 3 paragraphs that follow the Shema prayer in any Orthodox siddur.
The very powerful Psalm 91 is also included in all customs.
The Sephardi Bedtime Prayer also includes the beautiful and powerful Ana B'Koach Prayer, which has many beautiful melodies to sing it to. Ana B'Koach can be said any time of day for protection and inspiration.
It’s best to say it all with as much feeling and pleasure as you can muster.
Rav Fetiyah mentions that if you need to wake up at night because of a crying baby or to adjust your blanket or something like that, you should ideally say all of the actual Shema prayer again. And if you can’t, you should say at least the first verse which starts off as: “Shema Yisrael…” and then the second verse which starts off as: “Baruch Shem Kavod…”
Rebbe Nachman of Breslov passionately recommends reading from Likutei Moharan right before sleep for night protection and good sleep.
Rabbi Levi Yitzchak Bender emphasizes that saying the prayer “Hashkiveinu—Lay us down” and emphasizing the verse within: “V’taknenu b’aitzah tovah milfanecha—Set us aright with good counsel from before You” is particularly powerful for having a good day, with God’s Help, the next day.
(This prayer is also included in all Orthodox siddurs within the Bedtime Prayer.)
Saying specific Torah verses or prayers (as mentioned within whatever version of Bedtime Prayer you are reading) until you fall asleep is a good method for sweet sleep.
Performing self-introspection and a self-accounting as you fall asleep also sweetens one’s sleep and offers protection. This sounds counterintuitive because you might think of things you’ve done wrong throughout the day, which is unpleasant, but it really works.
Here are some sources:
Jewish laws and suggestions regarding Bedtime Prayer
Chabad/Lubavitch Insights and Suggestions for the Bedtime Prayer
Ashkenazi Krias Shema in Hebrew Only
The Shema Verse with Its 3 Paragraphs in English Translation
Ana B'Koach in Hebrew, English Translation, and Brief Explanations