What you can do: Make sure there are no visible lights in your room, whether from a digital alarm clock, TV, or light peering through your window. You can block out all light either through by adding blackout curtains to your bedroom or using a sleep mask.
The science: Melatonin is a chemical produced in the brain’s pineal gland at night time in order to regulate the body’s natural sleep/wake cycle. In the evening, melatonin production is triggered. In the morning and throughtout the day it is suppressed by light. When even a little bit of light is present in your bedroom (such as that from a window, television, or electronic device), melatonin production is partially inhibited and your circadian rhythm is disrupted (Reiter, 1991).