I've struggled with sleep for as long as I can remember. I have improved it considerably in the past year (still not perfect). Out of the dozens upon dozens of things I've tried, here's what I think made the most difference, in order of importance. 1. Very consistent bedtime and wake up time. +/- 30 minutes, but ideally less. Obviously if you struggle with sleep you can't count on falling asleep at the same time, but…
1) Melatonin 300mcg (2 drops) -- usually after 2-3 days, taking it I found I don't need it for another 3-4 days. No tolerance at 300mcg. I've tried other drugs that I still use for when I'm stressed (zolpidem which I actually like recreationally but won't take it when there are others in the house, antihistamines, or benzodiazepines).
I cannot stress how good it feels to know that I have options in case I can't sleep. The same with panic attacks I had a few years ago -- once I knew I had lorazepam/alprazolam in my wallet and I could end any panic attack in 15 minutes, the panic attacks stopped by themselves. Just having the option gives me peace of mind. The same for polydrug usage that helped with my BPD -- having the ability to just change the way you feel was such a blessing and the beginning of the end of BPD for me (70% was dealt with by therapy).
2) Actually fixing the problems in my life -- when I'm happy with my work, my child, my wife, I exercise a little (even just a bike ride in the park), I practice my hobbies, I socialize a little -- in such days I sleep like a baby.
3) The whole sleep sleep hygiene thing -- it's just a cherry on top of the cake, if I had a good streak of days where I was content/happy, I can basically do everything sleep hygiene says but in reverse and still get a great sleep.