Wake up at 8am tomorrow. You will be very tired, but stay out of bed. You want to be as tired as possible. Next night go to bed earlier and you shouldn't have too much trouble falling asleep before your job.

Also, if that doesn't work, don't worry too much. Your first day on the job is usually easier and you'll be able to pull through.

1. Do all the usual sleep advice: no caffeine the day before, no electronics in bed, no bright lights, etc. Make sure the only thing keeping you awake is anxiety.
2. If anxiety is the only thing keeping you up, then the only way to get sleep is to reduce the anxiety. Different things will work for different people, it's worth experimenting to see what works best. There are a million different ways.
3. If you can't calm down, just accept that you may not get any sleep. For the vast majority of situations, a night without sleep will not hurt you or your performance as much as you think. Sometimes the best way to calm down is to realize that the stakes are not as high as you imagined and that you are going to be okay.

All the "sleep hygiene" advice helps, but I also find listening to a lowkey podcast in the dark distracts and relaxes me. When I start drifting off I stop the playback and (usually) fall asleep.

Mantras.

As you’re trying to fall asleep, repeat in your mind ‘I will awake at seven alert and refreshed’. (e: or six or five, or whatever, but keep a rhythm.)

If your thoughts are intruding, say it aloud. Keep your phrase to four beats (awake, seven, alert, and refreshed should be even beats). Keep saying or thinking it, over and over, until you fall asleep. Sync it to your breath and heartbeat.

It sounds stupid and simple, but it works.

Melatonin

Paying attention to my breathing has sometimes worked (though not always) (not changing it, but feeling how your chest goes up and down and hearing the air rushing in and out and maybe even picturing the rhythm in your head). It distracts me from other thoughts and calms me down.

If that doesn't work, I try to distract myself with an interesting fiction book. That normally brings my head to less adrenaline-inducing thoughts (since now when trying to fall asleep I will be more focused on who the murderer of the dead child could be, or why the Zogophonts abandoned that resource-rich planet)

Cannabis, heavy indica. Some sort of Kush usually that I keep in reserve, I rarely smoke these days otherwise. Knocks me straight out in this sort of situation, great sleep.

Don't overdo it or you'll be all baked and goofy feeling, you just want to be relaxed and sleepy.