Armed forces use this method
Relax the muscles in your face, including tongue, jaw and the muscles around the eyes
Drop your shoulders as far down as they’ll go, followed by your upper and lower arm, one side at a time
Breathe out, relaxing your chest followed by your legs, starting from the thighs and working down
You should then spend 10 seconds trying to clear your mind before thinking about one of the following images:
You’re lying in a canoe on a calm lake with nothing but a clear blue sky above you
You’re lying in a black velvet hammock in a pitch-black room
You say “don’t think, don’t think, don’t think” to yourself over and over for about 10 seconds
Takes like, a month to get it on lock