Select an image of Paul McCartney to use for reference. Depending on the pose you intend to draw, you may want more than one reference image. Decide what era of Paul's career you would like to draw, for example the youthful moptop of 1964, the thoughtful songwriter of 1966, the ex-Beatle of the 1970s, the mature rocker of the '80s and '90s, today's elder maestro of pop rock, or some other moment of his long, distinguished career in music. Pick an expressive photo with a memorable feature such as Paul's smile or arched eyebrow.
Place a piece of tracing paper over your reference image. Break down the face into four or five main shapes, and trace them. For example, sketch a circle for the top half of his head, an inverted triangle for the lower half of his face, and slanted ovals for his famously droopy eyes. Repeat this exercise two or three times, searching for simple shapes in the image. Put the tracings aside, as this is a warm-up exercise to familiarize you with the underlying shapes of Paul McCartney's face.
Use pencil and paper to draw the main shapes of Paul McCartney's face, checking the reference image as you work. Erase and redraw the shapes until you have composed the overall layout of the face and head. Draw the body using the same technique, if you wish to include it, breaking the figure down to ovals, triangles and rectangles.
Add detail to the shapes, such as the curve of Paul's chin, the wave of his hair, the apples of his cheeks. Move your eye along each curve and simultaneously move your pencil along the shape, reproducing what you see, coordinating your eye and hand. Note the contour of his clothes and flesh out the shapes with connecting details. Modify each shape in the composition until it appears to flow smoothly, instead of looking like a jumble of shapes. Erase and redraw as necessary.
Draw in the details of the face, such as the eyeballs, the shape of Paul McCartney's lips, the dimples or smile lines at either side of the mouth, the smile lines by his eyes, and his expressive, often arched right eyebrow. Add details of his outfit, such as the famous early Beatles collarless jacket and the Beatles boots.
Note which areas of your reference image are dark, such as the hair, the pupils of the eyes, the eyebrows and any dark clothes. Darken them with your pencil. Cleanup any leftover guidelines with an eraser.