Step 1. I start from the outline of the eye. Please note that the bottom line is dropped and appears above, to show tear channel. I noticed that a lot of people forget to paint tear channel. Keep in mind that the eyes are different. This eye is my own. I think that my eyes a little bit rounder than usual:
And below is an example of how you should not draw the eye. ;) I saw a lot of people drawing such an eye. Sometimes they like to paint narrow eye slit with iris placed exactly in the center not touching the upper or lower eyelid. In reality you usually look at the relaxed eye where the part of the iris is hidden. Another problem with the picture below is that the lines of the eyelid are drown too clearly. There is no sense of form, because there is no change of width of the lines. Moreover, this figure does not show tear channel.
Step 2. And here I began to develop the shadows. I have allocated specific areas which I think is very important. Area #2 is usually ignored. It should be the light along the inner part of the lower eyelid. Look in the mirror at your own eyes: your eyelids aren't flat!
Step 3. Now it is the time for imposing shadows. There should be a good balance between light and shadow. Area #1 is rather important... A lot of people forget to impose shadows directly to eyeball and leave it entirely white.
Step 4. Using a thin brush, add the light in specific areas. You'll notice that the objects are becoming more clear now. Note that in area #2 illuminated iris is opposite to the bright white light stain. I heard that it is the way the eye is usually highlighted, but did not stick me on this. ;) Highlight the eyeball (area #3) some like in the previous step.
Step 5. We should deepen the shadows along the contour lines. I always obscure the pupil of the eye as well as the edges of the eyeball. I have noticed that pupils are obscured in the edges and in the center, then they fade to the center, where the backlight is becoming partly bold, eye color - more clear:
Step 6. The last step! I added beams in the center of the eye to make it more realistic. I also added a bright light to the tear channel. Don't forget that it is the wet surface so the part of your eye can shine:
Step 7. Done!