Here are some resources on how to craft real people out of paper and ink.
Querytracker. A great way to organize your querying process. The forums are where I found most of my crit partners, and the blog has useful updates on the publishing community.
Need more query help? Beside the QT forums above, also try Matthew McNish's Quintessentially Questionable Query Experiment. Super helpful, and a super guy.
Literary Rambles. Great resource on agents and new children's fiction and authors.
Laura Pauling. She has a great blog that discusses the hows and whys of plotting. Look up her plot-buster posts. They're awesome.
Is there shrink in the house? Laura Diamond is a psychiatrist who has a series on how to deal when your characters suffer from mental illness. Sarah Fine is a child psychologist who expertly analyzes so many behaviors we, and our characters, have. Both are amazing writers, to boot!
Adventures in Children's Publishing. Great resources here on the sidebars, great content.
Moody Writing. Written by a nice, mysterious person named Mooderino, this blog is spot on when it comes to writing advice.
Of course, there are the books.
Along the way, I've read Writing YA Fiction for Dummies (hey, I was curious, okay? It's super basic with some solid stuff you need to know); On Writing by Stephen King, Save the Cat by Blake Synder, How to Write the Breakout Novel by Donald Maass, James Frey's How to Write a Damn Good Novel (not that James Frey, the other one). All are really interesting and help you chip away some of the newbie mistakes that we all make.
Not one of them is my bible though. You really have to craft your own manual as you learn. That's the truth.
I also haven't yet mentioned the many, MANY books I've read in the genre I write. They are also my textbooks. I consume YA and MG fiction rather voraciously, and the lack of shelf space in my house can attest to this fact.
Find a good crit partner (or three)! And find a good support group. You'll need it. Because good writing doesn't happen all of a sudden, like riding a bike. It's more like riding the bike up Mt. Everest. Give it time. Let your writing breathe. Keep dreaming and write it all down.