The best way that did work for me is do not use alarm clock.

Setup a proper sleeping place first: a) it must be dark enough (if you close your eyes, wave your hand in front of your face and can see brightness changes, then it's not dark enough); b) it must be cold enough, and you likely need to have proper warm and heavy blanket; c) it must be quiet enough; if you have noisy environment, you can mask it by using source of monotonous noise; I've found, that air purifier produces decent enough masking noise; d) air inside the room must be fresh.

Then, take a break and allow yourself to sleep as much as possible without setting an alarm clock or having to worry about things to do. Your body will figure out sleep schedule automatically.