Practising 'mindfulness' techniques can help take focus from your mind and instead onto your physical body. This process can help with physical relaxation, promoting good sleep. Starting with your toes, take a few moments to focus on each part of your body, slowly working up towards your head and face.
Breathing techinques are a need. Also calm yourself before going to sleep. Turn your technology off 1-2 hours before going to bed. This will help you feel more tired and unwind. Also keep doing this in order to get into a routine. This way it will be easier to get used to sleeping at certain times, as by getting a routine, your body will get ready and prepared. Your body is programmed to routine. I also like to journal before going to bed as you can vent and then be calm and free in your mind before going to bed and sleeping!
The best way to stop ruminating about something that worries you in order to get a good night's sleep is to tell a close friend how you feel. You could get a better night's sleep by listening to calming instrumentals as you fall asleep, or maybe even counting. It's up to you.
The best way to stop ruminating about something is this: "Gratitude",being thankful about the outcome of the event ruminated is the best way to stop ruminating about anything.The slogan should be "Gratitude make it your attitude!"
It's a similar process to when trying to combat anxiety. Essentially it's about being in the moment. Rather than focus on the issue, tell yourself that there's nothing you can do about it at that exact time. It can help to schedule a time the next day when you will focus on the issue again. When you give yourself permission to stop worrying you will find relief and sleep.