Well, when painting anything, you paint the big shapes before the little shapes. So before doing any fur detail, I block out the light and shadows. When I get to the fur texture, I start with a few fur "shadows" (where the fur is closer to the skin) here and there, so get a feel for the direction and depth of the fur. The bigger fur "shapes" are blocked in the first (think sort of like loose clumps), and then the smaller fur "shapes" (smaller clumps of fur, or even individual strands if you desire). Hope that makes sense!