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.
For this exercise, I took a shot around Hucknall Train Station. For this shot I used a Canon 7D (crop sensor) with a Canon 70-300mm lens set at ISO 200 and shutter priority 1/1250, f/4.5, 100mm.
The following shot was taken:
Here the depth of field ensures that the subject matter is in focus but the steps in the background are very out of focus.