This is called "progressive relaxation" and though it might sound silly, it really works! I bet if you look around online, you can probably find a nice recording of someone calmly talking through the prompts to relax each muscle group. I was trained in how to do this during drama class in high school and it would put every single one of us in the class to sleep!

Good luck finding a method that helps you sleep... I tend to do a sort of visualization where I imagine tomorrow in excruciating detail, and usually by the time I get to breakfast (after getting up, making coffee, and showering) I've fallen asleep.