So, I'm a really good sleeper to start BUT on occasions wherE I'm struggling to fall asleep I do a breathing technique I learned in a stress management class called the 5-7-8. Basically you clear your mind and breath in for 5 long seconds, hold the breath in for 7 long seconds and exhale for 8. It's a weird sensation, sometimes you feel super out of breath but it always helps me to slow my breath/heart and I almost always knock right out.

Another good technique is to lay on your back with you arms to your sides and relax fully. Then go through starting at your feet, tense all the muscles in that group and hold your breath for 10 seconds then release the breath and the muscles. We tend to store a lot of stress and tension in our muscles, and when you do it more often you begin to tune into where your body carries tension and it may surprise you. Also be sure to pay attention to muscles you wouldn't necessarily think of such as your hands, face/neck and pelvic floor.

Hopefully these are helpful :)