1. One should sleep on the right side with placing the right hand under the right cheek.
عن حفصة رضي الله عنها زوج النبى صلى الله عليه وسلم أن رسول الله صلى الله عليه وسلم كان إذا أراد أن يرقد وضع يده اليمنى تحت خده ثم يقول اللهم قنى عذابك يوم تبعث عبادك ثلاث مرار. (ابو داود رقم 5047)
Hadrat Hafsa (Radiallahu anha) reports that when Rasulullah (Sallallahu Alaihi Wasallam) intended to sleep, he would place his right hand under his cheek and recite the following duaa thrice:
اللَّهُمَّ قِنِى عَذَابَكَ يَوْمَ تَبْعَثُ عِبَادَكَ
2. One should not sleep on one’s stomach.
وعن يعيش بن طخفة الغفاري رضي الله عنهما قال فبينما أنا مضطجع فى المسجد من السحر على بطنى إذا رجل يحركنى برجله فقال إن هذه ضجعة يبغضها الله. قال فنظرت فإذا رسول الله صلى الله عليه وسلم. (ابو داود رقم 5042)
Hadhrat Ya’eesh Ghifaari (Radhiallahu Anhu) reports: “On one occasion I was sleeping on my stomach in the Musjid due to stomach pains. Suddenly a man came and shook me with his leg saying: “Sleeping in this position (i.e. on the stomach) is disliked by Allah Ta’ala.” (I turned to see who was addressing me), then I saw that it was Hadhrat Rasulullah (Sallallahu Alaihi Wasallam).”