Dark Meditation
When you close your eyes, what do you see?  No, don't just say black because, because if you look closely, you'll notice that there is much more than black there.  What ever you see is called your "field," and this will vary from person to person.  In fact, what you see will vary from moment to moment.

One of the more interesting meditations that I've encountered uses this phenomena to accomplish several ends.  If you do this at night, when you are ready for sleep, you'll find it can be quite a powerful sleep aid.  It does produce other effects so continued use of it can only be beneficial.

The basic procedure is to lie comfortably on your back and close your eyes.  Concentrate on your field.  As you focus on your field, you'll notice variations in the color and texture of what you are "seeing."  Pick the darkest spot and concentrate on it.  As you direct your attention towards it, you will notice that it may change shape, move and even change color.  Follow it and simply keep your attention fixed on it.  At some point, it will change color (probably white) and vanish.  When this happens, find the darkest spot in your field and repeat the process.

If you do this, you will find that you get very sleepy and you will probably fall asleep.  This sleepiness is an effect of what is happening but can serve a useful purpose, i.e., getting to sleep.  Now, as you are doing this exercise, you may find that you get strange physical sensations.  You may become aware of odors that are not there, feel like you are floating or falling, or find memories springing into your mind.  The general rule is to keep focusing on the dark spot and not focus on the distractions.  Should you become too uncomfortable, simply open your eyes, and stop the exercise.  However, continue if you can.  If you work through it, it will be gone and that particular circumstance will not occur again.

There are those who make remarkable claims for this exercise and I'm inclined to think that it can have a positive effect on you other than getting to sleep.  Give it a try and let me know what you find its effect on you is.
This can also be done sitting up, or where ever you can relax and close your eyes.  It is best if you can remain undisturbed, but that's not essential.