Note: Before doing this, make sure you have a full stomach and are comfortable. It is much easier to concentrate when the body is calm.
Begin by picking a spot to relax in. This should be a quiet environment, where you will not be interrupted during your practice. Sit in whatever position feels most relaxed and comforting to you. Close your eyes.
Next, clear your mind of all thoughts, focusing on silence. After about ten minutes of this, focus on your chest area. Focus on the very center of it. You should begin to feel a tingling sensation, or possibly a cold sensation, building up in the middle of where you are focusing.
Now, mentally "push" and "pull" this feeling throughout your body. Work on bringing it up and down through your arms to your fingers, then pulling it back down and going out through your legs. After another ten minutes or so, you should have a chilly, tingling feeling over the parts of your body where you have been focusing.
You can do this for any length of time. Whenever you feel you've done enough, stop.