The eyes are, hands down, the most important and characteristic feature of manga characters, so we'll start with them. Manga characters are, by definition, set up to feature the eyes as the center of focus. Manga eyes are oversized, contrasting with the rest of the facial features, which typically get less detail.
To make the eyeball itself sparkle, you'll need to use contrast. That means you need to draw "shines" amidst heavy pools of black. Shines only sparkle when surrounded by dark areas. But if the dark area is pure black, the shines may end up looking light white spots, not reflective or moist, which is what you're after.
To lay down their eye shines, manga artists use solid black areas with streaked lines that mimic the look of irises. The results are so effective that the eyes seem to almost glitter. This streaked effect-- migrating out of the pools of darkness, combined with multiple shines of varying sizes-- makes the eyes really pop. In addition, note the naturla path that the eyelashes take, as well as the heavy lines of the eyelids.
Excerpted from Top Ten Essentials: Christopher Hart's Draw Manga Now! by Christopher Hart. Copyright © 2013 by Christopher Hart. Excerpted by permission of Watson-Guptill, a division of Random House LLC. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.