Every so often I'll post a link to various blogs that I think are especially good. One of them is Editorial Anonymous, the blog of a working Children's Book Editor. She usually posts about once a week and each message is dead on for people writing in this field. Click on her name to reach this week's message. Also -- Note what Rachel Stark says in the comment field about writers needing to practice their craft just like concert pianists do.
Or, as I remember Jane Yolen saying at a reading in New York City -- "How do you get to Carnege Hall? Practice. Practice. Practice."