Strong evidence, less costly:
- Combined aerobic and resistance training. Exercise at a vigorous intensity for 40 minutes a day, 5 days a week. Strength training at least 3 times a week.
- Meditate at least 20 minutes a day. Although most research focuses on mindfulness meditation, some preliminary findings suggest that Christians who practice centering prayers (basically a mantra meditation)show better stress management and less distress indicative of better executive functioning. I believe spatial working memory was one of the improved cognitive facets associated with mindfulness meditation.
- Antidepressants if you are depressed or anxious. Effects are not immediate.
Weaker evidence, less costly:
- Diet. I'm surprised how little good experimental research there is on humans, but studies on rats say that a high fat diet effects working memory and performance on the Morris Water Maze. High fruit and vegetable diet has the opposite effect on rodents. Most of the research on humans focuses on cognitive decline rather than cognitive improvement, but correlational studies suggest avoiding too much foods loaded in saturated fat.
Costly, and if you are going down this route please get it done by a professional. There is a lot of snake oil on the internet:
- Neurofeedback
- Transcranial magnetic stimulation