Hi Dan,
This thread is about horses but the concepts are the same:
Paint Horses Shep Paine wrote several books that are still available and they cover, again, predominately painting horses.
So a dog? Not to be silly, but what kind? F'instance, my sheltie had spots that were both hard-edged and had a gradation to the difference colors of fur. My beagle - I could paint him with hard masks!
Back in the 1980s Fine Scale Modeler had a series of modeling how-to's by some famous modeler, and he addressed painting critters. Depending on what color the fur is, the key to painting animals is capturing the sheen of their fur - even dirty fur. IIRC, he reminded people that there really isn't a true black in beast fur, it will be extremely dark brown or even blue. So the key is to add subtle highlights. Also, critter fur tends to be earthtones; looking at my beagle yesterday I noted that his fur is an exact match for fallen dry magnolia leaves. So paint beasts earth tones.
