Find a location with good light for a portrait shot. Place your subject some distance in front of a simple background and select a wide aperture together with a moderately long focal length such as 100mm on a 35mm full-frame camera (about 65mm on a cropped-frame camera). Take a viewpoint about one and a half metres from your subject, allowing you to compose a headshot comfortably within the frame. Focus on the eyes and take the shot.
I took this shot as instructed with a wide aperture, F 5.6, at 100mm focal length, one and half metres away and as the light was fading and the rain beginning, selected ISO 400. It was a fast shoot due to the rain, however I do like the way that the shallow depth of field emphasises the subjects face and blurs the background. I would like to experiment with this more for portraiture, to learn more about how the shallow depth of field slightly compresses the features and see how it can add intensity to the eyes, whilst lifting the subject from the background.