keep yourself warm. drink fruit tea (not black or green as they have caffeine in them), avoid caffeine in general.
listen to calm music, podcasts.
set yourself a strict regime. don´t go to sleep "just when I feel like it" this really ruins your sleep pattern. go to sleep at relatively similar/same time.
destress with whatever helps, again music, meditation, journaling etc.
don´t take short naps during the day. tire yourself.
try to watch your sleeping pattern for a week and see where is the problem.
Do you go to sleep at the same hours?
Were you stressed before you went to sleep?
Are you comfortable enough?
How many hours of sleep do you need? *
* Not everyone needs those 8 hours, especially the older you get, the less sleep your body actually requires. Maybe try sleeping less? 5-6 hours?
Now, if this is a long term, I´d consult your GP.