Upon arriving at مزدلفة after sunset from عرفة, the first priority is combining Maghrib (3 ركعةs) and Isha (shortened to 2 ركعةs) الصلوات. النبي (صلى الله عليه وسلم) combined these two الصلوات at مزدلفة with one adhan and two iqamas. This should be done soon after arrival — do not delay the الصلوات unnecessarily to settle in.
The requirement for staying at مزدلفة varies by school. The Shafi'i and Hanbali schools consider staying at مزدلفة even for a moment after midnight as fulfilling the واجب (واجب act). The Maliki school requires staying most of the night. The Hanafi school considers the stay at مزدلفة as واجب, and departing before Fajr without excuse requires فدية. The strongest practice is to stay from arrival until after Fajr الصلاة, then depart for منى before sunrise — this is the السنة of النبي.
During the night, collect 49 pebbles (or 70 if staying in منى for 3 days of التشريق) for the stoning ritual at الجمرات. Pebbles should be slightly larger than a chickpea. Sleep under the open sky — there are no tent structures at مزدلفة. Make دعاء and dhikr, especially at the Mash'ar al-Haram area. The night at مزدلفة is a profound spiritual experience of simplicity and equality, as all الحجاج — rich and poor — sleep on the bare ground together.