Often, the inability to relax stems from a racing brain. Getting control of "mind chatter" is more than half the battle. Here's what I do.

Lie down somewhere where you are unobstructed (like the back of a couch squishing your arm to your body).
On your back, totally relax all of your muscles. Let your arms and legs sink into the surface beneath them.
Close your eyes and concentrate on your breathing. Regulate it with slow breaths in through your nose and hold for a second, then slowly exhale out of your mouth.
Listen to your "mind chatter" for a moment. Are there a billion things running around in there?
One by one, let your thoughts go. Tell yourself you can take up those thoughts later on.
Try to clear your mind, especially of negative "mind chatter" and concentrate on your breathing.
Bring up a thought that makes you feel relaxed, like floating on a lake on a warm summer's day with the sun beating down on you, a gentle breeze blowing across you.
Think to yourself that you are perfectly calm and relaxed, totally healthy and happy. Let your "mind chatter" focus on those thoughts and nothing else.
Continue the slow breathing... in through the nose, out through the mouth.


It is hard to relax with "mind chatter". If your thoughts are racing in 100 directions, you can't relax. The key is to calm your thoughts. Your body will follow.
When in the midst of a busy day, you can still do this. If you are sitting at your desk, take a minute and close your eyes. Do the slow breathing and repeat your thoughts that you are perfectly calm and relaxed. Picture yourself in that place where you were the most calm and relaxed.
If you are having trouble keeping thoughts out of your mind, it may help to count your breaths. By focusing attention on your breathing, you become more aware of your body naturally. This may help it to calm down and settle into a slow rhythm.

If you're tense and all worked up about how this might be yet another failure, it will not work. These things take time and practice. Give yourself the benefit of the doubt and try it for a few days.