Counting sheep
(cliche, i know, but sometimes it works. it bores you to tears first, but eventually you can drift off)

Write a mental list of things you are thankful for
(some nights this is harder than others, but it helps build pathways of positive thinking. at least, according to psychology)

Think of all the things that made you smile today
(there will be days that this doesn't work, but it might just earn you one more smile on the better days, and whatever sleep you get'll be more restful)

Turn off screens, and keep electronics out of your room
(you're probably thinking oh now she's just being bossy or yeah, i've heard enough about this from the scientists but it works most of the time. try it)

Meditation
(people usually connect this to come religion or superstition but really it just relaxes your mind and body, slowing your heart rate and calming your thoughts)

h.f.m.