Repetitive actions increase serotonin levels in the brain, which helps mood and reduces stress. That is one reason why crochet is so relaxing. I crochet sometimes. I also play instruments, so practicing helps sometimes. (Other times, if it is actually the music stressing me out, it doesn't help.) Other repetitive motions might help, too. Most crafts would fall in this category. If you like to write, typing out what you write might help, instead of writing by hand.
When I was younger and had a little more time to myself, I would put on some music I liked, lay down, and focus on *one* line of the music. It could be a voice or an instrument. I personally liked focusing on the bass line. I would focus so hard on just that one instrument, I basically fell asleep and when I woke up, my mind was empty. It worked freakishly well.
I also took many baths.
I go by myself to my favorite quiet places (I did this more before I had kids, and am doing this a little more now that they are teens.) It could be a walk in the woods, or down to the beach to watch the waves. Something where there is something gentle outside of myself I canfocus on - the rhythm of the waves, the sound of the breeze, birds tweeting, etc. The clean air of being outside in nature helps me breathe deeply, too.