There are several things a rookie writer must do to become a seasoned author (other than writing, that is.) Reading "how-to" books, attending conventions, reading in your genre, reading out of your genre, and learning about the industry in general are all excellent uses of your time. If you want to be a better writer, though, forget all that. The best way to get better is being read.
"But, Kelly," you say, "I want to be published. That's why my butt's in the chair three nights a week. How do I get read if I'm not published?"
Ah, Grasshopper. Those shiny books on the library and bookstore shelves were all read several times before they ever crossed an editor's desk. Here's the secret: behind every successful author is a posse of alpha- and beta-readers. These readers are in the trenches--they find all plot holes, misspelled words, and continuity errors before anyone else. They'll tell you if a sentence--or a whole chapter--doesn't make sense. They are invaluable to the writer. To find them, look no further than a trusted friend, co-worker, a local writer's group, or a fellow writer you got to know at a convention.
Here's the rub: if your first reaction to joining a writer's group or asking a co-worker to read your stuff is "Uh, yikes," you're probably not ready. And that's okay. Keep writing, and someday you will be. Be aware, though, that in order to become better at your craft, you have to be willing to expose your story, warts and all, to people. You might think you've written the next The Eye of the World but what you've really written is nowhere close to that, and you've got to get your ego out of the way long enough to realize it. You are not perfect. Everything you write is not awesome. However, your alpha- and beta-readers will point out your strengths and your weaknesses. They will help you get your work as close to awesome as you can.
This might not seem possible now, but the more you have people read your stuff, the easier it gets. You'll say, "Tell me what you think," and you'll mean it. You'll get to a point where you hand someone a story and say, "Rip it apart, baby," and you'll be disappointed if they only have a few suggestions. You'll keep writing, they'll keep reading, and you'll get better.