StepsDress for bed.
When you are about to go to sleep, put on your favorite pajamas. Choose the sleepwear that makes you feel the most comfortable - avoid anything too tight, itchy, too cold or too hot.

Go ahead and lie down on your bed or chair and close your eyes.
Imagine a night sky, with small, chubby, white stars, and a crescent moon.
Or, imagine a day sky, with a small, green hill, full of short, luscious green grass that sheep would adore.
Imagine a white fence right across the hill.
Visualize white, fluffy, plump sheep.
Imagine the sheep jumping over the white fence, one by one, one after another without stopping.
Visualize this over and over again, counting, "1.. 2.. 3.. 4.. 5.. 6.." softly. Some people prefer to count in their mind, others out loud - this is up to you.
Drift off to sleep gently. If you get sidetracked and the worrying thoughts return, take stock and return to counting the sheep.
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Tips
If there are lots of sounds around, imagine some cows in the distance making that sound.
If there are people around, (eg. on a plane, downstairs, outside your window) don't count aloud. Just imagine a number showing underneath each sheep as it jumps on through your visualization.
Another theory is to change the moon into the shape of the number each time.
This might take some practice.
You can substitute any animal for the sheep; you may be more comfortable with goats, zebra, llamas, cats, dolphins etc. Obviously, you will need to adjust the visual landscape accordingly and the action of jumping over something may not suit all animals.

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Warnings
Counting aloud may make you look foolish and it maight distract others.

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Things
You'll Need Bed or chair (Sleeping area)
A good imagination
Good focus