The absolute hardest thing about painting a pet portrait for a pet owner is getting a good reference photo of their pet. Try to get as many photos of the owners pet as possible. Then choose one that has the best lighting and composition, and watch out for the markings on the pet. The markings on a pet which will probably be big contrasts of light and
dark areas can sometimes cause problems with the form and shape of the pet. Look for overall good form and lighting on the pet. A big problem with pets that are all black and have shiny fur is you loose their shape, so make sure you have good lighting that shows form.
Drawing the pet portrait is also very important, being off just a little can change the total caricature of the pet. If you need to use a projector because your drawing skills are not totally
developed, then by all means use this machine to get your drawing of the pet perfect. The owner wants it to look like their exact pet, not a portrait of that breed of pet.
Don't change your style of painting when doing a pet portrait. Paint in the style you normally paint, many students tend to tighten up when painting a pet portrait trying to make it look like a photo. Make it look like a painting in your own
style.