Instructions:
Now. Here's the real trick. Even though we'll detail the entire hair, there's no need to super-detail all of it. Pick out one lock that will receive the most attention. Everything you do to the entire hair, you'll do twice as much to this strand. The texture and detail level of this one lock will have major impact on the rest of the picture even without everything else being quite so detailed. Just trust me on this one.

I'll pick the lock falling down along the side of her head. Once you've got a lock singled out, use a spackled brush and veeeery light pressure to softly follow the flow of the lock down to where it ends. Repeat over and over again in short strokes -- and keep your finger on the colour picker ( the alt key while you're using the brush) to use the right colour in the right place. This way, you will bring out the shape of the lock while keeping the separated, thinner sections The spackled brush will help to, even at this early stage, add some nice texture.

Common mistakes:
Unnatural fall. Take some time to study how hair actually falls. How the curls or locks wrap themselves and how they affect one another. Unless the hair is heavily styled with lots of hairspray and fussing, there are some things it generally won't do.