Seven habits worth the effort, backed by research.
Get outside within an hour of waking. Real sunlight, even on a cloudy day, beats indoor lighting, and this is what sets your internal clock via the suprachiasmatic nucleus.
In the evening, dim things down for an hour or two before bed, screens especially.
Wake up at the same time every day, weekends included. Sleep debt isn't like financial debt: you can't really pay it back, and shifting your schedule around just confuses your body more.
Cut caffeine at least 6 hours before bed, longer if you're a slow metaboliser. Its half-life ranges from 2 to 10 hours depending on genetics, so it lingers more than it feels like.
Last drinks at least 3 hours before bed. As your body breaks down alcohol overnight, you get a "rebound effect" that fragments sleep and cuts into REM, leaving you groggy and short-tempered even after a full night's sleep.
Keep the room cool, somewhere around 16–19°C. Your body needs to drop in core temperature to fall asleep. A warm shower about 90 minutes beforehand helps, since it pulls blood to your skin so you cool off faster once you're out.
Don't use the bed for anything other than sleep and sex, so your brain doesn't link it with lying there awake and stressed. Not asleep after 20 minutes? Get up, do something dull, come back when tired.
Do the same few steps most nights, so your brain learns to recognise them as the signal sleep's coming. If your mind races with to-do lists, dump it all on paper before you lie down.