Brush the hair downwards with a body brush, then do sweeping movements towards the tail to create the effect. 1st one straight across, then on angled 45o to it, then next straight across etc...
Got these pic off another site a while back, which you might find explain better.
Each new brush stroke is the hatched area, and the diagrams follow on from each other -
Finish it off by using the brush to brush downwards.