Falling asleep can be the toughest part of the entire night. I have a very active mind, hard to shut off some nights. What I learned, with some reliability and success, was to build something in my imagination, or to run through all the steps in a process in order that they need to be performed. This type of cognition seems to lull me and I'm asleep, most often, inside of a few minutes. So, cold-firing a steam locomotive, or setting up a telescope and getting it polar aligned, or imagining I'm explaining to someone the processes going on in stellar interiors. There's a lot of knowledge in those, and some things have to take place before others. This iterative thinking can lull one into sleep.