Move away to small towns.
Seriously, with modern city stress it is normal to be bad sleeping habits. Recent study shows that even highschool students have only an average of 6.5hr sleep when they need 8 to 10, not to mention adults. Moving away from the source of stress ie, cities can make it easier to improve sleep durations and qualities.
But, nobody does that cause its pretty unrealistic. So a more common idea wold be:
Treat sleeping as a duty, just as important as school and work. Make a plan, follow the schedule, and keep it every day.
You might have to sacrifice other things to get the allotment to work, but we all only have 24 hours per day, so it ultimately just means "how important is sleeping to you?"
Like right now, you sleep @ around 3 or later, and plan to wake up after 9. So:
a) What keeps you up till 3? Why do you need to wake up at 9?
c) Do you feel the current schedule is working fine? (Not all people need 8 hours sleep from 10 to 6 after all. It might just be that it is working for you.)
d) If it isn't, is it possible to readjust your "up till 3" thing? Either stop it, change it, or shift it for after you wake up?
e) Same with "wake at 9".
f) Assuming both are immovable, can you set up "nap times" during the day to make up for it? (Current theory is that as long as you get 8 a day, when you get it isn't as important. Though preferably you should get your REM cycles uninterrupted.)
g) What sort of food habits you have? If its not what you do that makes you sleep late, there are many cases that it is caused by food habits either in type and/or hours.
h) If it is neither habit nor food, then maybe it has to do with health? There can be physical or psychological reasons. Or if you don't have those, there are over the counter meds that you can take short term to help you retrain your sleep schedule.
g) But anyhow, you do actually train how you sleep by choosing when to sleep. The habit of sleeping@3 means that once you get used to it, that makes your body harder to sleep in other hours (ie. circadian rhythm / biological clock.) You fix that by doing exactly the same thing: Making a habit of sleeping at the hours you want to until it sticks. And like all trainings it takes time and effort.
Light exercises, wake up duties, hot milk, etc. Can all help you sleep, but the most important thing is making/keeping a habit of it.
(I have Sleep Apena and need to wear a machine to sleep, and my med makes me wake up after 4-5 hours, so I kinda did some research on the topic before. v=3=v )