For me, a 37-year old teenager, the best thing I've ever done to improve my sleep was setting "downtime" (in iOS screen time settings) from 21:00 to 07:00, and ask my partner to set a screen time password that I don't know so I can't cheat. Works wonders! It creates just enough friction that I don't want to reach to my phone or a computer (which is in another room), and still allows for handling emergencies since messages and phone calls still go through.