The wonderful Gail Simone offers brutal tips for breaking into the comic book industry. Everything she says is true, especially the parts about having to be more self-critical of your work and to be able to bring something new to the table.
One of the mistakes some folks make is to read a bad comic — and there are many out there to choose from — and to say, "I can do better than this." That's probably so but it doesn't make you qualified. As my pal Len Wein often notes, an editor is not looking for someone who's better than his worst guy. He's looking for someone who's better than (or maybe just as good) as his best guy.
And to all of that, I would append what I say these days, which is that it's foolish and not worth the effort to become a comic book writer or artist. What's not, assuming you have the ability, is to become a writer or artist who works in comics among other things. The construct of the current business is not all that friendly to the creative person who only aspires to do comic books. In fact, there are some powerful people who almost count that against you because they want to think of their company as bleeding seamlessly into film and television and videogames and other media.
But read what Gail has to say. It also helps to be as good at what you do as Gail Simone is at what she does.