No visible clocks. If possible don’t check the time at all while trying to sleep. Doing math at night (aka “oh no only 4 hours left”) only makes you angry or sad.
No alcohol. If unavoidable, try to be sober by the time you want to fall asleep. (Dring sooner, if at all.)
No coffee after midday. Some bodies suck at metabolising it.
Bedroom should be as dark and silent and comfy as possible. If there’s any way you can add comfort, do it.
For persisting sleep problems: Change position or location. (E.g. turn completely around in your bed, feet at the headrest, or sleep on the couch if comfortable.) Brains are very good at linking a location with a state of mind, and changing things around can help if the thought of your bed stresses you out already.
For severe problems it’s probably always wise to check with a physician, or if there’s specific stuff in your head that keeps you awake to consider telling a friend or therapist about it. To distance yourself from your thoughts is something everybody can learn and it can be tremendously helpful with stuff like that.