Learn the rules. Inhale the rules. BE the rules.
Because only once you understand the rules, may you break them.
The greats who break the rules regularly can do so because they know what those rules are, and know why they're breaking them. That's what makes them great. Breaking rules because you don't know they exist just makes you uneducated.
When you're just getting started in this wild and wooly world of writing and publication, you have to know your craft. To steal from another blogger: You wouldn't want a doctor who doesn't know anything about bones, nor a lawyer who decides to study the laws after passing the bar, would you? No! Don't try to become a published author on sheer ideas alone.
You can have the best idea in the world, but if your technical ability blows, you'll never get past that agent's assistant. The world is full of many people who think they can write; don't be one of those who blames the publishing industry for the fact that they suck.
Also understand that you're not as good as you think you are. Just because your family, your friends, and your dog tells you that they love your stuff doesn't mean anyone else will. I know I'm a good writer... but I also understand that I have a LONG, long way to go before anything I write is publishable. To quote Hemingway: "The first draft of anything is shit." That also means the second, third, and fourth drafts will probably suck, too. And that's okay. As long as you never reach Anne Rice proportions and decide you're too good for editors, you'll have a chance.