The hair is a frequent point of difficulty for beginners because it requires the most amount of patience. All shading for the hair should be done in soft lines that are close together, varying in intensity, and the direction of the pencil lines should always be in the same direction that the hair flows in. The first area to make note of is the part: the area which the hair splits into different directions. The strands will form and inward curve towards the scalp, thus it will get dark near the part, hit a highlight at the curve, and move into a medium to dark tone. It is essential to have that highlight or the hair would appear flat. Other parts will vary in intensity depending on the subject, so be observant on that point.

Shading in the wrong direction: always, always, shade in the direction that the hair flows. It may seem easier to create a horizontal band of darks with horizontal lines, but it will look incorrect. Pencil lines define hair, thus it would look awkward with any other direction of shading.

The key point is to be observant. Identify the lights and darks and put them in, and above all, be patient! You don't have to put every single detail in there. Hair is still hair if its missing a few curls, but value, texture, and direction of your lines are essential. In cases where hair is extremely frizzy, you don't have to include the value of every strand, but in most cases, hair closer to the face is darker, so those are the values that you should be looking for.

There are three common mistakes in acheiving a realistic look for hair:

Smudging: never blend the shades of the hair. You have to try your best at getting various tones, and having them translate from one tone to another naturally. Hair does not have the same smooth texture as the skin, so smudging is not a good method of blending in the tones.

No tone: a lot of people tend to consentrate on the fact that hair is made of strands, and as a result, we get a mass of flat lines hanging down from a three dimensional face. Hair has values, and it is essentail to get those values in there. It is tedious, but the values are essential for a realistic portrait.