Off the Bookshelf: WRITING GREAT BOOKS FOR YOUNG ADULTS, by Regina L. Brooks

Subtitle: Everything you need to know, from crafting the idea to getting it published.

Very thorough, very useful, very well-organized.

The chapter titles say it all (and lots of examples and even explanations of why you shouldn't do something):

Five Rules for Engaging Readers of Young Adult Fiction

Meeting Your Characters

Building Your Plot

Setting the Timeline

Learning to Write Dialogue

Getting Constructive Feedback

And the appendices:

Feedback Resources

Publishing Processes at a Glance

YA Publishers

And more than what I've listed.

If you want to learn about it or NEED to learn about it, here's a great foundation for either starting out writing, period, or switching your focus from another genre/market/audience.