When drawing a portrait, it is very important to be able to trace the eyes in a realistic way.
Steps
Method 1 of 2: Drawing with the Hue Overlay

Step 1. Draw the shape of the eye

Step 2. Add details for the pupil, iris and eyebrows

Step 3. Trace the eyelashes, pupil, iris and eyebrow reflections

Step 4. Lightly shade the drawing to simulate a faint shadow

Step 5. Complete the drawing with a darker pencil and fill in the areas where the shadows need to be more intense
Method 2 of 2: Draw by Adding Layers of Gradients and Shadows

Step 1. Trace the shape of the eye
Use magazine images as a guide for drawing various types. This is the first step you need to take.

Step 2. Now you can draw the pupil and iris

Step 3. Go to additional details

Step 4. Use a darker shade to go over the design

Step 5. Shade the whole eye with a light gray pencil

Step 6. Darken the barely shaded areas further

Step 7. Color the darker portions with a deeper shade of gray

Step 8. Now darken further with the gray pencil the areas that are to be heavily shaded, but not completely black

Step 9. Blur the edges of each shading layer to make the drawing look realistic thanks to these different levels of gray
Advice
- Practice makes perfect.
- If you draw a girl's eyes, draw thicker, darker lashes.
- Don't overdo the definition of the lashes, otherwise you will get a weird looking eye.