You already know it should be dark, but it should also be quiet and cold like a cave. Thermoregulation influences your sleep cycle. Essentially when it’s time to sleep your core body temperature should drop. If your room temperature is too high it makes it difficult for your bodies temperature to naturally drop.
The ideal temperature for your room is between 18- 20 degrees. A warm shower or bath can also help drop your bodies temperature drop- just be mindful as a shower just before bed can sometimes wake you up.