Reciting the Adhkaar (supplications) mentioned in the Sunnah before sleeping.

There are a number of Adhkaar prescribed in the Sunnah before going to bed, amongst them are reciting the last verses of Surah Al-Baqarah Verse 285 and Verse 286], reciting Surah Al-Falaq, Surah An-Nas and Surah Al-Ikhlas. [Saheeh al-Bukharee and Saheeh Muslim]