What can I do to relax before going to sleep?

I've started having a warm drink half hour before bed, putting my phone on charge, (out of the way!) and reading a book in bed instead. So far so good!
I'm still finding what works best for me, so you probably need to try a few things too. But whatever you try, I'd suggest starting the process half hour before you actually shut your eyes.
If you're a stress head like me, maybe some meditation would help. I also find I can't switch off if I get straight into bed, so maybe making a list or a plan for the next day would help get things out of your head and ready to sleep. Hope that's some help. Good luck, and sleep well!

I have worked hard to help improve my sleep. The 1st thing that made any significant difference for me was listening to sounds that help focus brainwaves down into Delta Waves. That helped tremendously. Doing EMDR for sleep as I settled down to rest was great to put me into and keep me in a deep sleep. Cautious here though. You don’t want to stay in EMDR longer than recommended and you don’t want to drop into it initially without a qualified EMDR Institute Therapist to help you as it can have strong side effects. Sleep Stories has been another source of great help as it allows my mind to get lost in something good. Winding down with a PM Yoga Routine and Meditation has also made a difference. As you can see, I’ve tried many things but it is the building of a sleep routine that has made all the difference.

You can do some deep breathing exercises.
Do some reflective journaling.
Could read a calming book.
Listen to a podcast.
Or maybe do some meditation guided.

Stretching really helps me. Youtube has tons of videos in before bed stretches. I also use mood lighting and not bright overhead fluorescent lighting. I have a salt lamp and I use that along with a diffuser so set the mood of the room to peaceful for resting

Put your phone away, your tablet, your electronic gadgets, everything of that sort. Groom yourself and/or take a warm shower or bath. You probably heard these a lot of times but they're really important, trust me. 🙂 If the next day is an important one for you, prepare everything you need if you prefer so. You can also consider reading physical books to wind down after your shower if you're not sleepy enough, as doing that is much, much better than mindlessly scrolling through your social media. In my case, working (or basically just being active) during the day also helped me feel tired/relaxed enough at night, so falling asleep is somewhat easier.

First of all, I would recommend some sort of routine that will tell your body and mind that it's time for bed soon. I make a cup of tea, go to my room and read for about half an hour. After that, I put on a sleep story on my meditation app and I usually am asleep in less than 5 minutes.

Calm your mind by turning the lights off and setting a time on how many shows I watch or how long to use devices for. Drink water and pee. Maybe read, imagine yourself asleep. Tune in on the day before and the day ahead and plan maybe. Journal or write out any emotions that come up. Sing out the stress. Or dance. Yea

Try Yoga. Or a good book on paperback. Anything to get your mind off the anxiety. And remember that it is just sleep. You need at least 7.5 hours of it. So match your alarm clock accordingly, or take a weekend and don't match it to see how long you do need to sleep a day.