I used to set an alarm every night in bed for 7-8 hours later, relative to whatever random time I was getting in bed. For years the only advice I ever heard in terms of sleep quality was "getting a good 7-8 hours", so this led to years of awful sleep.

Now, I set an alarm once and don't ever touch it again. It goes off every day of the week, weekends and all, everyday at the same time. And it's been one of the biggest and most directly noticeable changes I've ever done for my routine and wellbeing. Sure, sometimes I go to bed late and I don't get my 7-8 hours, but for the first time since I was a kid I feel sleepy at night and it doesn't take 1+ hours in bed to fall asleep.

If anyone reading is in the same situation I was, please try it. Even of you usually wake up late, even at noon or later, just wake up at the same "late" hour everyday. "Early" doesn't matter. But after a while you can make small 15-30 minute changes in the wake-up time every month to two months or so, if you wanna start waking up earlier. If you still have trouble falling asleep, even some light exercise like a light walk around the block, helps a lot, particularly if you spent the day sitting.

Maybe this is super obvious for most people, but it wasn't for me, so it might be helpful for someone else.