Once you are stressed start relaxing the different muscles in your body... this may sound difficult as you will have to park the emotions a side for a few minutes. Start relaxing your facial muscles and then neck, shoulder etc., By relaxing you are teaching your body to distress.
Listening to music is also a stress reliever. When you are tensed start listening to some music and remind yourself of some good memories. Music can calm your mind and body and also helps lower blood pressure.
Exercising is also a stress buster. It provides dual benefit of retaining a trim body as well as calms the mind.