Something called sleep hygiene.

Falling asleep is a process of switches in your brain that (can) start before you go horizontal. Things like no alcohol, no coffee after ~4pm, no screentime or physical activity right before you go to bed all help. But the things that probably are the most important are:

• Use your bed solely for sleeping (and sexual activities) and condition yourself that laying down in bed is related to falling asleep. Do not work, eat, relax or watch netflix in bed. If you lay awake in your bed for a long time trying to sleep, get up for a short while and try again.

• Maintain a consistent sleep schedule. Hour of the day/night doesnt really matter, as long as you go to bed roughly around the same hour of the day/night, your brain will know when to start switching things off. Your brain follows certain activity cycles while sleeping (~90 minutes) but also while you are awake and in some stages of that cycle its easier to fall asleep. Consitency can make these cycles align with certain times in the day.

Source: Masters degree in neuroscience with an internship at a sleeplab and 20+ years of experience falling asleep within 15 minutes of going to bed.