Go wide for an exaggerated effect
Wide angle lenses aren't commonly used for close-up portraits, as they exaggerated a person's facial features in a way that is usually unflattering. With animals, however, the exaggerated features can look humorous and create a unique shot.
Include some environment in the shot
Step back and ask yourself if the space around your pet would help make your photo more interesting. I think the shot above would have been much less interesting if I had just focused on Casey's face.