The publishing business is a furnace. That may sound metaphoric, but it's almost too true to be a figure of speech. Every time I send out a manuscript, it's going to go through fire. If I've tempered it myself, then it might survive, but if I've left it with weaknesses, it will be consumed by the fire like chaff.
Remember the space shuttle Columbia? It was a beautiful ship, but during the takeoff of its final mission, a small hole was poked in one of its wings by a piece of insulation that fell off a fuel tank. The hole was hardly noticeable, but it mattered when Columbia faced the heat of re-entry. The spaceship broke apart, tragically killing all of the crew.
The hole in Columbia's wing can be likened to flaws in your manuscript. The publishing industry is choosier than it used to be. Despite this pickiness, most of the books which are chosen for publication don't pull their weight financially. Publishers rely on the ones that do, which is why they are so careful. If you're frustrated by this, don't be. Just deal with the holes in your writing so that you won't burn up when you go through the selection fire. I believe these are some of the keys to surviving the flames.
• Study English
Yeah, I know. You thought you were done with school. Maybe you had the idea that writing (especially for kids) was going to be a shoo-in way to earn a few extra bucks and get your name in print. Not so.
You're going to have to study if you want to be good enough to make it past sharp-eyed editors, because in addition to that trifling thing called plot, editors care if you misspell words, don't know a compound sentence from a misplaced modifier, and sprinkle adverbs and exclamation points through your story at will. If you send out a flawed manuscript, I see a form letter in your immediate future.
• Read everything that editors, agents, and successful writers have to say about writing and publishing
This requires further study. There are lots of books at the library that will help you, or you can pick up some at your local bookstore. I check them out first and buy the ones I think are most helpful for later reference.
This is important because if you're not willing to take the time to research what those experts want, you might as well paste a huge sign on your head that says, "I DON'T KNOW WHAT I'M DOING, BUT I JUST WANT TO PUBLISH A BOOK." Don't waste an editor's or agent's time. Take up knitting instead.
• Join a writing group
Your family loves you. At least, I hope they do. Unfortunately, they aren't reliable when it comes to telling you the whole truth about what you write. Also, if they aren't writers, the likelihood that they'll know how to make a manuscript better is pretty slim. Writing group members are more objective, and they have your best interests in mind. Find a group to link up with and be glad they've got your back.
• Reach out and touch someone
The best place you can go to make contacts is conferences. They're not only learning opportunities, but places to meet established publishing professionals. Before attending, study to find out how to make conferences pay off for you. If you're financially strapped, try to get to one of the smaller local conferences. One published author told me that she preferred the smaller conferences because she felt like she got more out of them.
• Writing is a job, so expect to work hard at it
Don't just think this publishing thing is going to happen to you because you have good intentions. One established author (I think either James Scott Bell or Randy Ingermanson) said that you can expect to devote four years of consistent writing and study to the craft in order to be a serious contender as a writer. That's not unreasonable when you think it's also the amount of time it takes to get a degree from college for most careers. Writing is no different. Writing is all about content, not intent. Do what it takes to make the content great, or get out of the slush pile.
Now for the encouragement.
Don't worry about what might or might not happen. Write your book, because if you don't write it, you'll never publish it. That much is certain. The sooner you begin the process of developing your craft as a writer, the sooner you'll become better at it, and hopefully, the sooner you'll end up published.