First, easy one, if by some chance you still have one of the old-style bulky CRT monitors for your computer, or use one at work, give it away today. Those things used to be the bane of my existence, just made my nerves buzz endlessly. Thankfully they are mostly long gone.
Beyond that, below find quite a few possible techniques for shutting it off and sneaking into dreamy land. Some nights I have to try quite a few of these; some nights none work and I have to invent another one. Mix and match, good luck. The main idea is to displace the left-brain verbal chatter with nebulous right-brain activity, way more likely to calm the hell down and give it up. Give your thoughts something steady to focus on, or try to get involved in passive observation, and next thing you know you're waking up going, wow, I guess something must have worked.
First, get your body receptive. Lay on your back, with a pillow under your thighs, and pull your head pillow close under your neck so your head is supported and your throat opens. Turn your hands so your palms face up, in a position of surrender and receptivity. Uncross your legs and ankles, and let gravity just have you: sink into the bed. If you find any tension, fill it on the next inhale, and let it go on the next exhale. Another option is to move your feet slightly apart and let your raised knees fall together, then cross your arms over your chest so your elbows almost touch; I once read this position is supposed to be less physical effort than laying flat.
Alternatively, roll onto your belly, with a pillow under your hips (roll it double if necessary), and another (or two) lengthwise under your chest, arms wherever they're comfortable, at your sides, above your head, or crossed under your chest. Your neck will feel more open if your head gets no pillow, but just falls off the top edge of the pillow under your chest. This position is harder on the lower back, but sometimes when it's all too much, it can feel a bit nurturing and enclosing, allowing you to ground your stress into the bed. It helps relieve pressure on the lower spine to move one leg up, bending the knee out to the side, and turning your head to that side. (Look at my yoga page for remarks on spinal alignment, etc.)
If you prefer to lay on your side, pull your legs up a little and put a pillow between your knees to keep your hips stacked. If your hips are much larger than your waist, you might want to try a small pillow under your waist to keep your spine from sagging. Keep the pillow under your head tucked up close under your neck so your neck can stay straight.
Gentle music can help; you aren't going to do much better than DJ Olive's gentle Sleep and Buoy records. My Deep Ambient mix is pretty hypnotic too, and my hour-long piece novameria is very tranquil. There are also lots of gadgets on the market that generate soothing sounds like waves and rain.
-A simple yet so-effective yoga breathing technique for reducing anxiety and calming the mind is called Ujjayi breathing (OOJ-eye). It is so unfamiliar and clumsy at first, then after a bit it's second nature, effortless. Breath evenly in and out, flat and level, and work out how to make a gentle hiss on both strokes. You will get a little stoned. This is developed a little more on my yoga page. Try it anytime you think of it during the day.
-Thinking of things, words, events (imaginary or otherwise), people (same), fantasies? imagine instead objects, hold them in your mind, turn them, transform them. Especially look at the spaces inside them, the negative shapes between and around them. This switches off the left brain and lets the gentle lazy right brain do its thing.
-Imagine an active populated scene, like a restaurant. Call up say, a table and a couple and a waiter, plates and glasses and everything. Then, move your eyes quickly like 30 degrees to the left, and, without thinking, just look and see what's there, then move them to the right and look and see what's there. The idea is to jump from active imagination to passive looking at a scene that has a life of its own. As soon as something happens on its own, if you pull yourself from the scene, you'll feel that little twinge that you get when you suddenly awake from a daydream. Three of those and you'll feel noticeably rested. Sometimes. If you can manage to get sucked into passive looking and stay with it, you might just find yourself waking up hours later going wow, whaddya know, it worked.
A variation on this, takes some effort, is to imagine you are at the front of a train, going down tracks through a landscape. As best you can, pick up speed, so much so that the landscape comes too quick to control. Again, the idea is to start with active controlling imagination, and slip into passive observation of a scene that has its own life.
Another variant is to try to imagine a magazine or book, and read it as quickly as you can, just let your eyes scan over it, let the words become whatever, just stay with it, until you go from active to receptive imagination.
-Visualize your body, just try to get the shape of it in your head, feel your toes, your elbows, your hair, your mass and its shape, let your attention take that shape. Then, when that's working okay, visualize the bed. Don't rush to the next step, and if you slip off and your head starts spinning, backtrack, start again, as necessary. With increasing success, continue through the stages: the room, your apartment, the building, the block, the neighborhood, the city, etc. If you focus on it, you won't get much past the immediate vicinity.
-Breathing is such a powerful thing to focus on. The air we breathe contains so much undifferentiated energy; if you don't tune to that, you miss it, but if you give it some attention, you begin to feel how much potential it contains, pure life. You can't keep it; you can only open to it for the brief time you have it to interact with, then it has to go to wherever else it's off to. Let your eyes go soft; let them lazily point at a spot somewhere off the end of your nose. Idly watch down the sides of your nose as the breath goes in, mingles, goes out, pause, that same cycle over and over, never reaching anything, endless, infinite, made up of present moments that do not last. Any tense areas, fill them on the inhale, then gentyl contract the area on the exhale, and say farewell, making room for the next swirl of local infinity. With focus, you can find your whole body buzzing with relaxation before long. Give in to gravity, just fall, letting the tension drop through the bed.
-Relax your toes. Don't rush it. Then, relax the balls of your feet. Then your arches and tops of your feet. Then the ball of your heel. Then gently move the relaxation around your whole ankle. Take your time, really let your attention go into each of these areas; think not so much of forcing the relaxation as releasing any tension you find, again with the filling and farewelling with the breath. After a while, you'll feel a gentle buzzing. Continue on up as best you can, adding little sections at a time, and if you slip off, backtrack as necessary. At some point start again at the fingertips, and move up the arms, eventually connecting to the torso, then the neck, then the head. If you're still awake at this point, just continue in passive awareness/visualization mode, filling tension with breath, letting it go. You can get pretty loopy in this exercise, almost an out-of-body experience.
-Eat some sugar. You will buzz for a bit, then a half hour later you will plunge into sugar shock. Go to bed immediately; it won't last. Other than this trick, avoid eating before bed, for at least a couple of hours before. Drink a glass of water instead.
-The traditional yoga exercise at the end of a session is corpse pose ("one day we will all be asked to let go; this is a rehearsal for that moment": how beautiful is that?), aka savasana (pron. sha-VA-sa-na). The main component of this is a technique that is so simple, yet so difficult: witness consciousness, whereby whatever is happening in your mind, you do not judge it or attempt to redirect it, you simply withdraw back a step and observe it. If you find yourself becoming involved, and you almost always will, just return to the exercise, and withdraw, withdraw, withdraw. it will seem so unfamiliar at first, and it is unlikely you can ever approach mastery: just keep withdrawing whenever you can, back, back, away.
A variant is to attempt to ignore your senses altogether: whatever body aches, mental hamsterwheeling, whatever, just insist that it couldn't possibly be of interest, even disdain and reject it. As best as you can, continue this in the odd states you will emerge into, for as long as you can. If you slip off, who cares, just try to ignore it again. This is an interesting meditation on its own, really unpredictable what odd spaces it can take you into.
-Take a shower, then get into bed without drying off. You will go into a slight shock as your blood abandons your organs and heads for the surface to warm you.
-Listen for distant, quiet sounds, like a major road five blocks away; try to visualize the distance, and try to really focus your attention there.
-If you really just can't sleep, then get up and do something. Turn on the light and read a book. Something to occupy your mind and displace the runny chatter. Read a boring book that will just soak it all up and leave you drained. Also works combined with the sugar trick above.
Just taking a proactive role in the situation can help ease the frustration, that turns into annoyance, that turns into anger and adrenaline, that just guarantees you are going to lay there fuming. If that happens, withdraw, observe, don't care, detach, slip out and watch it from a distance, maintain focus without effort, be firm but gentle, and hopefully soon the sunshine will greet your rested self.