For me to shut my brain down I have to have my TV on and my music going. My brain will actively tune out the noise because I can hear it the instant my brain clicks on in the morning. A bit like putting up a window blind. The trick for me is with the TV and music, it cannot be new. It has to be shows I've seen a thousand times or a song I've had on repeat for ages. If it's new I actively listen. Like right now, I need to switch over from Hoarders to Ghost Adventures and go to bed.
Put on a movie or series you always fall asleep to while wanting to watch it. (Works as a mental cue.) With my mom, she falls asleep whenever we watch LORT. How you can sleep through the Balrog, an orc hoard, and a fool of a Took I will never understand.
Start a bedtime routine. Essentially shutting down the household for the night. Our house: Dogs go out @ 8, fed @ 9, crated @ 9:15. Bathroom routine @ 9:30. In bed @ 9:45. My phone is plugged in far enough away that I have to get out of bed to get it. I do have to keep my tablet plugged in within arms reach for cardiac tethering, but I keep the notifications turned off. Its interface is also not as fast or as smooth as my phone, so I'm less prone to browse on it. Mostly it is for reading when my angina wakes me up at night.
Regular exercise during the day can also help, a lot. I walk between 12,000 and 20,000 steps over the course of a work day, but it ramps up during the holiday season. Even if I am physically to the point of crashing, I don't let myself have a nap because if I do my brain will be on and wired for the next 48 hrs. If that happens I will end up with a meltdown.
Everyone's brain is unique, but having a routine that signals your brain to start the shutdown process it can help. Disrupted sleep patterns are very common among NDs. Trial and error is the only way to find out what works for your situation.