Have someone help you hold and position your pet.
Put your pet on a table or get down on the floor to photograph him. Get on his level.
Make sure there is very good light. In order to paint detail, I need to see detail.
Does your pet have a toy or pillow that is never far? Send a picture of that along as well.
Get close for details of the face and muzzle. Eyes really are windows to the soul.
Photograph your pet in familiar and comfortable surroundings and casual positions.
Take several pictures in different positions and lighting to capture your pet's individual character and color.