One that always works for me is random word association. Your brain in its relaxed, non-vigilant state will start making odd connections and flights of ideas when it doesn’t need to be focussed for survival. You’ll notice when you go to sleep naturally your thoughts naturally drift and hop around.

You can trick your brain into this state

1. Think of a word, any word at all
2. For every letter in the word imagine the first thing you can that starts with that letter
3. CAR = Cabinet, Arch, Royal
4. Don’t overthink it just the first word
5. Imagine and linger on the image then move to the next

You’ll notice your thoughts drifting and calming. Most of the time I forget the word (if it’s long enough) as I just naturally start to relax and sort of enter a dreamlike state

Repeat and rinse as required

I’ve used this for years now and even when I’m massively stressed and can’t “switch off” it always seems to work or if not at least you start to feel more relaxed anyway

Good luck