Focus on a single image for a set length of time, in a quiet place.
The image could be abstract, a piece of art, a photograph, a stained- glass window, a sculpture, a carving, a tapestry, etc.
Focus all of your attention on the image. Notice everything about it: shades of light & dark, lines, shapes, colors, as well as what the image makes you feel. A 5-minute time limit is a good length to begin with.