An even simpler idea is to draw a set of lines across the form of any animal or person. It’s a quick way check the placement of all the features. If they’re out of position, you’ll know right away.
In these zoo sketches of a hippo, each head has a set of parallel lines to make sure the ears, eyes, and nostrils are kept in their proper relationship. In the top sketch, I’ve also lightly drawn the center line of the form. I tried to simplify the lighting by massing the shadow as a light, uniform tone.
In the lower sketch, I simplified the forms a bit (note the spherical forms around the eyes). The shading lines follow the cross-section contours, which helps even more to describe the form.
