Some people think the road to publication is a straight line. I tend to think of it more as the path Billy follows in your typical (though not especially funny) Family Circus Cartoon. Whatever route you take, you’re making the journey, and here’s a list of sites/people who can help.
SCBWI: Join. They have lots of advice, information about the market, information about different publishing houses, etc., for people who are just starting out. Plus, SCBWI can help you find a critique group in your area. The message boards are also extremely helpful.
Harold Underdown’s guide to publishing: Harold is legendary.
Agentquery: A searchable database that helps you find out about agents, according to what and who they represent. Find one you’re interested in? Look him/her up on twitter. Find some interviews and read them. It’s all about doing your homework.
411Kidlit is a helpful website, and answers questions you didn’t know to ask.
Ask the Agent: Rookie mistakes and advanced writer mistakes averted here. Your questions answered.
Writer’s Center: Bethesda’s Writer’s Center has some awesome classes, and I’m sure you can find some good classes near you, too, if you’re not living in the DC area. A class is another place to meet like-minded souls. Then you can form a critique group once your class is over, and keep going.
Paid critiques: There are lots of writers, editors and former editors, such as Tamson Weston, who do thorough, honest critiques of your work for a fee. You can also get short critiques at most SCBWI conferences. (I also do paid critiques but currently am only doing them for picture books.)
Poets and Writers Magazine: A great publication, with a classifieds section that can give you ideas of where to submit. (Grownup stuff more than kid stuff, mostly.)
Your local library: Spend some time browsing through the stacks so you can really know what’s out there and where your manuscript fits in before you submit.
Your local bookstore: Ditto.
The blogosphere: Kidlit bloggers are out there in force and they’re a great portal into super-smart discussions about trends, issues, what’s good and what’s bad. Visit the kidlitosphere for an introduction.
The first step toward publishing is writing, but writing is only part of it. You have to research editors, markets and agents. Do your homework. Nobody else is going to do it for you. Believe me, I much prefer the writing part, but that other part? It’s important, too.