I've been through phases of waking, wide awake, most nights at a specific time interspersed with the occasional full night's sleep. I've developed plenty of theories about what causes it including stress, late cup of tea, hunger etc. I've addressed it by getting up for the toilet then reading, going through karate kata in my head, among other things. These worked sometimes to get back to sleep but not to prevent the waking.
The situation is now reversed. I sleep well most nights, regardless of late cups of tea, with the occasional early hours wake up. Here are my strategies:
# No tech in the bedroom.
# An actual, physical book to read.
# Good curtains to block light from outside.
# I can't get to sleep if my feet are cold so I wear socks until the bottom of the bed has warmed up.
# As I switch the light off, I tell myself three times I will sleep now and wake up at a specific time. Amazingly, this works quite well! You don't have to believe it will work.
# Lately, a lavender pillow spray is working well for me. I don't care if it's a placebo or even a simple coincidence. It's very pleasant and I'm sleeping well.
# If I do wake and go to the toilet, I try to manage without switching lights on. Lights wake you up. When I get back to bed, I lie down straight away and tell myself I will sleep now.