What is the most important part of sleep hygiene?

Dark and quiet: No lights, no smart phones, no tv, no stimulants. Establish a routine and follow it. Avoid napping before bedtime. No late exercise? Just a few things o consider

Better Sleep Hygiene: The most important part of sleep hygiene is avoiding the things that interrupt sleep such as caffeine, alcohol, nicotine, excess food or exercise too close to the desired sleep time. It can also be helpful to keep the same environment and sleep schedule to develop a good sleep-wake cycle.

Quiet/ dark: You have received great info. I would say that if i had to make a priority - it would be quiet & dark environment. Here are more: retire & rise same time each day. Keep bedroom dark & cool & use only for sex & sleep. Turn off tv. No naps. Exercise regularly but not in late evening. No caffeine for 6 hrs & no alcohol or tobacco w/i 2 hrs of sleep. Keep dinner moderate sized & finish at least 2 to 3.