The direction is always toward the tail. Think of a windshield wiper. The direction is either horizontal or vertical. A variation is strumming or ruffling. Bend your fingers as if strumming a banjo.
Direction is either clockwise or counterclockwise.
Start with finger pads, and, as you get comfortable, change hand parts for a new style. Depending on the area, flick with one, two or three fingers. Start with feather-light pressure. With your hand in a horseshoe position, reach down into the fur and add a small pull on the return stroke. This works great from the neck all the way out to the tip of the tail.