Avoid caffeine, especially past noon, as its effects can linger long after you've finished your coffee fix. Also, while a nightcap may seem like an appealing way to unwind, alcohol disrupts sleep quality so is best avoided too.
Eating a large meal close to bedtime will keep your body awake and active when it should be winding down. Likewise, try not to go to bed hungry either - a growling stomach isn't conducive to nodding off! A light snack an hour or two before bedtime is probably alright, but definitely avoid anything too filling or substantial.
Keep the bedroom cool, dark, and quiet .
Try some deep breathing exercises just before sleep - this can help calm the mind and signal to your body that it's time to relax and switch off.
If you're on your phone, laptop, or watching TV right up until you close your eyes, try and leave some space between screen-time and sleep. The blue light issue mentioned above is a real one - give your eyes a break from screens at least half an hour before lights out. You could incorporate this downtime into your routine by listening to some calming music, meditating, or doing some stretching - all of which should help relax the mind and body.
Finally, try to maintain a consistent sleep schedule wherever possible. There's nothing like regularity to help train your body into a reliable sleep pattern.