I have lots of brilliant ideas that are as good as or better than what's being published. How do I get a job writing comic books?
The most accurate answer to that is, unfortunately, "You probably don't." Like any allegedly-glamorous career, there are always a lot more applicants than there could possibly be openings. I say "allegedly" because, at least at the moment, the job is probably a lot less than is envisioned by most of those who aspire to it.
Please read this carefully: The comic book business is presently in a lot of trouble. Sales are lower than anyone ever imagined they could sink. A lot of companies have folded, a lot of comics have been cancelled and a lot of those that remain are shaky. You would be amazed how many seasoned, experienced comic book writers (and artists and letterers, etc.) are not able to get enough work to make a decent living…and even most of the ones who are currently working do not presume it will last and are investigating other avenues. Given the difficulty of breaking into comics and the relatively small security and rewards, it may make more sense for you to invest the time, energy and talent in trying to crack a healthier field.
Yes, the companies do go through the motions of looking at samples (art samples, mainly) and they sometimes take on a newcomer. This is not because they're looking for folks who can do the kind of work they've been publishing but because they're searching for that next great superstar who will develop a following that sells comics. They want to snag that kid before the competition can get him.
If the preceding does not discourage you: If you are to have any chance of procuring employment, you need to strike that difficult balance between writing the kind of work that publishers know and appreciate…and bringing something wholly new to comics. Too much of either extreme will not do it. You may think, "I can write just like my favorite comic book writer, Sam Shmidlap." Well, perhaps you can. But you need to understand that they've already got Sam Shmidlap and, odds are, he ain't getting enough work. They don't need an imitation of him. At the same time, especially when you start out, you have to fit at least vaguely into the field as it exists. You can't revamp comics, or expect them to be revamped for you, when you're brand-new.
There are basically three ways in which writers in comics get hired. One is that they go to work for the company in some other capacity — as interns or assistants, for instance — and then move laterally. There are very few of these openings (less than there have ever been) and they rarely pay well enough to allow you to relocate to the city where the company has its offices. They certainly do not provide any sort of security or guarantee.
Another method is to submit manuscripts. This rarely pays off. (You wouldn't believe how high the pile of submissions is in most offices. And since they don't need new writers, there's no rush to whittle it down.) This usually involves submitting outlines for stories, hoping you'll happen on something that grabs an editor's eye. Keep in mind that certain comics have regular writers so if you submit plots for them, you're trying for a job that isn't even open at the moment. Also keep in mind that everyone wants to write Batman or Spider-Man or the X-Men and that these are rarely entry-level assignments.
Studying the comics will tell you the names of the editors and their addresses. Following industry news should give you a sense of what comics aren't committed to one specific writer. And if you can't figure that out, you probably don't know enough about the field to work in it.
The most successful method — and it ain't too successful — is to do something for one of the smaller publishers. True, they pay almost nothing (sometimes, they pay nothing, period) but at least, getting something in print will set you apart from all the wanna-bes who've never had anything published. And if you can't get the bottom guys to publish your work, you're probably not good enough to get the top guys to buy it, either. This method may involve you finding an artist collaborator and turning editor and/or publisher. But if you can do something outstanding in the farm leagues, it will get noticed in the majors.
I'm sorry this is not more encouraging, but I have been in comics since 1970 and have never seen it as difficult to break in as it is at present. It's even difficult for a lot of folks who have broken in and who were, just a few years ago, deemed good enough to get steady, high-profile assignments. There simply is not enough work for them, let alone them and all the new people who want to get into the field.