A simple technique to relax your mind and train your attention.
Play the sound file above and listen: Every few seconds, you will hear a soft click sound. Each 18th click has a different, distinct sound.
Count the clicks, quietly in your head, so that you can tell in advance when that 18th click will appear. Count quietly, don't speak. Visualizing each number will help.
When the 18th click appears, notice whether your counting was actually at 18 and start the next round, counting from 1 again.
Repeat for as long as you want. 5 minutes, 10 minutes, or more.
This easy technique will both help you relax and train you attention skills.
Calming your mind might help you prepare for sleep.
Over time, you will learn not to follow each random thought that comes up, but let it go.
Put the sound file on your iPod/MP3-Player or mobile phone.
The first few rounds might be relatively easy and you will correctly predict the 18th click. But then your attention will start to wander, so that keeping track of the sounds will get harder. Thoughts will arise and deter you from the counting.
So your prediction will be wrong sometimes: Maybe your counting was only at 15 when suddenly the 18th click appeared. This means you must have missed a few clicks -- maybe while thinking about your last breakfast or fantasizing about your next holiday. That's no problem and completely expected.
Don't blame yourself. Just bring back your attention and start again with the next round.
With headphones, you can easily do this on the train or in a waiting room. No one will notice that you are training you mind.
If you use the technique to prepare for sleep, set the volume very low, so that you will not be woken up should you fall asleep, but high enough that you can hear the clicks comfortably.
Visualizing the numbers while counting provides some redundancy and therefore helps a lot: On each click, imagine the respective number appear in a bold white font on a black background: 1 2 3 4 5 ...
Then try visualizing not the digits, but abstract sets of points, like the numbers on a dice. This might even improve your math skills by developing your sense of cardinality of sets.Find out which kind of visualisation works best for you.
After some practice, see if you can do without counting "one, two, three, ..." in your head, but just visualizing each number: 1, 2, 3, ... I find this way more interesting.