I'm a sucker for children's book historians (I have a Leonard Marcus cardboard cutout in my office!) and Martha Rago starts this session off with words from a favorite. A TOTAL CHILDREN'S BOOK BAD(er)ASS, Barbara Bader. Barbara contributes to THE HORN BOOK, which should be the first magazine you subscribe to if you are serious about having a career in children's books.
She's also the author of the excellent AMERICAN PICTURE BOOKS: FROM NOAH'S ARK TO THE BEAST WITHIN, a book well worth the wait and weight if you can find a copy. Martha riffs off a quote of Barbara's to get us thinking about what illustrators need to do make their final artwork sing and the resulting picture book stand out.
Here are two of those things, briefly:
1. Consistency of style. You can have more than one style, but they must all be strong and consistent. Martha's examples of illustrators with consistent styles:
2. Technical skill, you must master your technique! Susan Jeffers is a great example of someone who's mastered their particular media (medium?), in Susan's case, watercolors: