I'm pretty mild-mannered when it comes to advice, even when delivering "the bad news." One of my students called me "An iron fist in a velvet glove," which I found first startling, then complimentary, then -- pretty much true. The Keirsey Temperament Sorter, of which I am highly fond, affirms that my strongest category of intelligence is the diplomatic variety. I find myself paying a lot of attention to exactly how to word things to gain a certain impact on a particular listener or reader.
Diplomatic Disclaimer: Writing goals come in all types and stripes, and all of them are valid. You may have taken up writing because you've always wanted to give it a shot, because you just want to learn more about effective writing, because it's an outlet for expressing your feelings and/or creativity, because you want to write stories for the grandkids, because your family is bugging you to record their history and you want to do it as skillfully and entertainingly as possible, or for other reasons that are all your own. Any reason to want to write is legitimate (assuming you're not aiming to destroy the world), and I say dive in and have fun!
But, you say, you want to be a professional, publishing writer. (There's a deliberate order to that. Professionalism almost always precedes publication, unless you are paying a company to print anything you produce, in which case it may or may not.) Since you want to be a pro, and you want to get commercially published, let me offer my three-point overview to Get Your (Ca)Reer in Gear.
1. Get your writing into the middle of your life instead of on the fringe. Let's say your life is a city. Your job, family, home, church, and places you do business, pursue recreation, or serve your community are the downtown and residential areas of that city. Where's writing? On the outskirts? In a suburb? Scrabbling on the edge of a cliff hanging on by three fingernails? Leave it there for much longer, and it just might ker-splat into the gorge, glut itself on brats and beer and take a much-too-long nap, or stick out its thumb and hitch a ride on the Road to Elsewhere. Rescue the poor thing. Give it a home, a job, a time and place to function. You've got to. Even if something else (starting with the TV set) has to get run out of town on a rail to make room.
2. Read in the genre(s) in which you are writing. Yes, begin by reading, period. But move quickly to the specific types of material you want to write. Read them without ceasing. Know that field. You've got to. Even if something else (starting with the TV set) has to be ignored to make room.
3. Do the research. Study successful published books that are a lot like yours and notice everything: overall length; number of chapters; chapter lengths; how many main characters; frequently used ideas; cliches; how many different ways there are to start a story; how the beginning hooks the reader (or does it?); types of conflict (e.g., more outward conflicts for mid-grade, more inward conflicts for young adult); number of subplots; boy vs. girl characters; first-person, third-person, present tense, past tense; and on and on. The idea isn't to find the formula; it's to show you what's been done (and overdone), what's possible to do, what hasn't been tried yet, and what's truly different. Get up-to-date "how to write for kids" books from your library or bookstore. Study the writers' boards on the web. Go to a conference. Take a class. Visit publisher websites. Read their catalogs and guidelines. Do the research on today's school curriculum, sports, hobbies, geographical locations, how stuff works, and anything else you need to authenticate the background, details and action in your story. Don't assume fiction doesn't need research, and don't assume you can fudge because the story "is made up anyway." You can't. Do the research. You've got to.
Do these three things for a week, and you'll already notice a difference. Do them for a month, and your writing will be a vital component of your life. Let them be the iron foot in a velvet boot that gives you a welcome kick in the (ca)reer.