Draw the Outlines:
Sometimes I draw the eyelid edges first, then the iris, sometimes the iris then the eyelids - it works either way. I usually draw the iris as a full circle then erase where it overlaps the eyelids, so that the shape is correct. Then I draw the outer eyelid edges and any folds or creases around the eye.
Shading the Iris:First check for any highlights cutting across the eye surface, and lightly outline these. Shade the iris using directional shading to mimic its radiant patterns. Shade the pupil too, establishing good, solid darks. Watch out for highlights across the pupil too - if they are there, put them in.
Often artists use a bit of license when drawing the pupil, making it larger to give the person a friendlier look (since the pupils dilate when we are pleased to see someone), and making a highlight curve across it, to emphasize the shiny curved surface of the eyeball.
Shading and Shadows:
Now I'm adding some shading to the drawing. I add a fine layer across all of the inner white of the eye, and very, very lightly across the outer one. The 'whites' aren't really white, but slightly shaded. Reserve pure white for your highlights as much as possible. I add a layer of shading to the upper eyelid, an some shadows around the eye. At this stage, the shading is quite strong - I'll soften it with an eraser. (Bear in mind that the scanner hasn't picked up the lighter tones).Smoothing the Shading:
The eye drawing is almost finished. The shading in the eye is completed, making sure the white highlights are crisp. Notice the shadow drawn under the upper eyelid. This helps to give it a more three-dimensional look. Skin tones require a fine touch with shading. I use an eraser to lift excess tone, sometimes re-drawing several times until I get the subtle shading that I want. I've made the shading in the whites of the eye a little darker so that the highlights look brighter.
Notice that I haven't drawn the eyelashes yet. I want to be able to smudge and erase the tones on the eyelids without disturbing the eyelashes.
To finish off the eye drawing, I've softened some of the shading further to create quite a smooth effect, and crisped up the highlights in the eye. Then I've added the eyelashes. Look carefully at the eyelashes - note where they start. A common error is to have eyelashes growing out of the middle of the eyelid. A few hairs straying inwards, but most eyelash hairs grow quite precisely out of the front edge of the eyelid. Use an almost flicking motion, lifting the pencil towards the end of the hair, to draw the natural taper of the eyelash.