Get on their level. Crouch down so that you can hold the camera straight.
Bright and Beautiful! Good lighting is crucial to a painting. The best place to get good lighting is outside or near natural lighting.
Get the whole picture! If you want a full body portrait, the artist needs to be able to see your whole pet.
Stand at the right distance while taking a picture. Stand close enough to see all detail; but not so close that the picture seems distorted.
If you want multiple subjects in one picture, it is best to get get both pets in the same shot if you can.
Don't Stand Above your pet or angle your camera. A birds eye view can make a nice photo, but it doesn't make a great painting.
Don't use flash and avoid taking pictures in lower lighting or rooms without windows. Not only does it hide detail, but it can make your pet look like a slightly different colour!
Don't crop off anything you want included in your portrait. The tip of an ear is fine, a whole leg is harder to create. Remember that large objects in the foreground can cover your pet up just as much as cropping.
Don't get too close! Your camera will distort your pet's gorgeous face!
Don't stand too far away while taking the picture.