Sleep Hygiene (also commonly referred to as bedtime habits or routines) refers to all the practices and activities necessary for you to have "normal", quality nighttime sleep and full daytime alertness. We all have sleep hygiene, but not everyone has good sleep hygiene.
Those with good sleep hygiene follow consistent routines and have behaviors that allow them to fall asleep, stay asleep, and get a full (restful) night of sleep. Those with poor sleep hygiene often have erratic sleep schedules, have difficulty falling asleep, often wake during the night and are unable (or have trouble) going back to sleep.
Good sleep hygiene is really important because it helps prevent sleep disorders, and promotes healthy sleep and daytime alertness. Good sleep hygiene includes having a consistent routine, going to bed at the same time each night, not reading or watching tv in bed, only going to bed when tired (associating the bed with sleep), and so on.