Now that you've got the basic structure of the hair and put in the darks, you've won half the battle. Drawing lifelike hair is in part a test of observation, and in part a test of patience. This approach will certainly work for quick sketches when applied judiciously, but for really lifelike hair, you will need to take your time and pay attention to detail.

Now draw the mid-tones, with pencil-strokes following the direction of hair. Draw the darker lines separating sections of hair, and patiently draw the dark areas showing behind lighter hairs. At this point I use a harder pencil over the darks, filling in the paper-grain and blending the tone out along the hair. For super-smooth and shiny hair you can use a blending stump along the hair.