That looks fantastic so far! Great job!
I have a tip as well... although it's more of a cheat.
Like AF said, do a dark eye first, and then paint the eyeball white. But what I often do for the pupil... is to use a very fine-point Sharpie permanent marker.
Hey, as long as the result looks good, anything goes, right?
Good suggestion. I want to emphasize what I said earlier about a vertical line for the iris/pupil. You want the top and bottom to touch the black "eyeliner." If you look at a normal human eye, you don't see the top and bottom of the iris because they're behind the eyelid. If they don't touch, it will look like the character is surprised and eyes wide. (similar to what happens if you don't do the eyeliner at all)
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