That's it for the initial sketch! From this point on, press harder with your pencil to get a more defined sketch.
Step 11: Lightly sketch an oval inside the head, near the top edge, for the eye. When you get the shape and the position of the eye right, darken the lines. Shade the inside of the eye except for a tiny circle off to the side to represent glare. Add an extra-dark value to the middle of the eye for the pupil. Draw a few more lines around the pegasus' eye for the detail on the folds of skin.
Step 12: Draw the nostril near the bottom of the muzzle as a curved line similar to a backward letter C. Add some value to the left side of the curved line. Add a longer curved line on the right to complete the shape of the pegasus' nostril.
Step 13: Darken the U-shaped guide to create the pegasus' muzzle. Add an extra bump on the left side for the other nostril. Follow the basic path of the guide but curve the line upward before it hits the right edge to create the mouth. Then draw a curved line under the mouth for the lower lip.
Step 14: To create the shape of the pegasus' ears, darken the triangle-like shapes on the head but make the lines curvier. Add a curved line inside each ear to further define the shape.