3 things for me that help clear the fog: 1. Nutrition, diet. Cut bad sugars and fats, increase protein (necessary for 2.), keep balanced meals, take vitamins and minerals if necessary. 2. Exercise. Aerobic (running, swimming, cycling) and anaerobic (weightlifting, pushups, squats). 3. Relaxation and rejuvenation. Meditation, massage, chillout/lounge music, fiction reading.

For more information there are plenty of books on amazon.com on these topics.