1) Choose a person, older than yourself, you see frequently — not too often by approx once a week or once a month. Maybe one of your grandparents if they are still alive.
2) Every time you meet the chosen person you press your 2 pointing-fingers firmly against your eyes for 10 to 20 seconds until various colors and patterns arise.
3) Try to note or memorize the patterns and colors in connection with the context and repeat the practice every time you meet the chosen person for a as long as possible, minimum 6 months.
4) After minimum 6 months of this practice you can recall the person, virtually by pressing your eyes for a while. In the midst of the colors and pattern a sense of presence of the chosen person arrives even after the chosen person has died.
Hans Ulrich Obrist, Do It