(1) Stay away from bright lights. Turn off the lights in the house. Particularly avoid blue light. (Put tape or nail polish over LEDs. Use transparent red tape if you need to still read the display.) And yes this means you need to get the fuck off TD and go to bed.
(2) Exercise. Allow 30 - 90 minutes between exercise and bed time if you can but if you're up late and can't sleep, burn some calories. Avoid eating shortly before bed to prevent blood sugar spikes keeping you up. Alcohol will raise your blood sugar also and potentially over longer periods, so try not to drink before bed.
(3) I dunno about you, but for me caffeine is something my body reacts to more the older I get. I used to avoid caffeine within 6 hours of bed time. Now I'm up to 10.
(4) Do something boring that requires mild concentration. Sometimes I play sudoku, picross, or read textbooks on algebraic structures. Focusing your mind quiets the more exciting thoughts that lead your mind to wander while focusing on something a little boring causes your mind to wander a little - but less. This is exactly the sort of state of mind that leads to dozing / dreaming.
(5) Even if you're not tired, it helps to just lay down and close your eyes.
(6) Most supplements and herbs have done absolutely nothing for me, but l-serine 30 minutes before bed has made falling asleep much easier for me. I stir it into a little unsweetened yoghurt. It still won't do anything unless I actually follow the advice in step (5) above.
(7) Have a kid. Pretty soon you'll find it much easier to get to sleep. It's the staying asleep part that gets harder.
Well look at that!
Even the woke Wikipedia police haven't had time to censor this information yet.
By the way the exercise doesn't necessarily mean exercise to the point of exhaustion. 5 minutes of compound weightlifting movements can be enough to deplete glycogen stores and cause your muscles to draw sugar out of the blood and prime your body for rest.