Stress is caused by resistance to thoughts. Do not live in past or future. Live in the present moment. Never identify yourself with the 'thinker' (mental dialogue). Never resist to thoughts and just be an observer. If you identify the thoughts as you, then you are unconscious and leads to all kinds of sufferings. Best way to be present is to observe the emotions and the environment around you. If you find mismatch in thoughts and emotions, thought is illusion and emotions display your true issues etc. Live the life with positivity and experience the happiness now, not future event or past.