i used to leave the door of my bedroom open to the hallway and kept the light in the hallway on and the door cracked. it let in a little bit of bright light to keep me feeling safe and as i got more used to the dark i either dimmed the light in the hallway or closed the door a little bit more. now i can't sleep with the light on at all.
reading a happy book that takes your mind off imagining bad things might help too, if you don't mind falling asleep reading.
good luck!