Get a copy of <A HREF="http://www.amazon.com/exec/obidos/ASIN/1582971897/ref=nosim/madhousemanor" target="_new">Writer's Market</a> (your local library should have a copy of the current edition).
Look for publishers who publish the kind of book you've written.
Go to a bookstore. Find publishers who actually have books on the shelves.
Using those two pieces of information, make a list of who you'd be happiest to be published by. Get those publishers' guidelines. Follow the guidelines explicitly when you're submitting your work.
Writer's Market has a number of useful articles in addition to the market listings.
Educate yourself about publishing. This is a business, this writing. It's up to you to learn as much as you can about the business you're trying to break into.
A compelling story compellingly told trumps nearly every other consideration. Work on your craft. You don't just have to be as good as the people who are currently being published, you have to be better (for some value of "better") to be picked up.
Remember, every single author who has a book on the shelves of your local bookstore was once an unpublished first-timer.
A good publisher gets books onto the shelves of doors-and-windows bookstores without the author's intervention ("listed at Amazon.com, BN.com, and on the publisher's website" does not cut it). A useful agent has sold books you've heard of.
Aim high.