I used to need an alarm every day to wake up; I no longer bother to set one at all unless I need to wake up at an unusual hour to catch a plane or something.

I managed it by spending about six months going to sleep whenever I was tired and sleeping until I woke up. (This was triggered by major physiological trauma I was recovering from.)

At first that meant I was sleeping 14+ hours a day. (Typically in two shifts, so that I had a few hours of wakefulness in the morning and a few hours in the evening.)

By the time I recovered enough that my body only wanted 8 hours or so, my habit was to go to sleep around 10pm and wake up around 6am. I managed this because my recovery was my #1 priority... more important than socializing or staying up late doing other things.

When I started living a more balanced life, I started staying up later, and found my balance-point was going to sleep around midnight and waking up around 8am.

That's still where I am. When I indulge myself and stay up late, I still wake up around 8, though I sometimes choose to nap for another hour or two and come to work late. (Admittedly, when I've gotten enough sleep I sometimes choose to not-nap for an hour or two and come to work late anyway.)