start with blocking in the darker areas, then turn your brush down to about 28-35 opacity, use the smaller 3 point brush and paint in each layer; then you have to get creative, brushing in layers to go from dark to light...use the multiply, burn, screen, and vary the lighting on differnt layers just to add depth. Hair on the top layer should be drawn in using the finest brush size, 1. remember not very many hairs are just straight, they are sometimes very messy so your brush strokes should be different...just keep building the layers...