How does one get their book published?

Seriously consider self-publishing. http://www.createspace.com/. You can also do an e-book through Amazon. An audio book. Etc.

First: Write the book. Next: Buy the most recent version of Jeff Herman's "Books, Publishers, Editors and Literary Agents". Next: Buy Larsen's "How to Write a Book Proposal". Next: Edit the manuscript, once by you and another by someone who knows the mechanics of writing very well. Next: Form an outstanding, catchy query letter, instructions for which you can find in Herman's book or any number of other books instructing you how to do that. Next: Send the letter and/or book proposal to all the agencies that are SPECIFIC to your type of novel. It helps if you select a particular agent within each agency who specializes in your genre.

You will receive at least 94% rejections or no replies. If you know anyone in the publishing industry, find out what specifics are working today. If you are fortunate to get an agent to read your manuscript, don't start celebrating. Nurture your relationship with these people. Be prepared, if somebody decides to publish, to go to book fairs, and book tours ... on your own dime. Be prepared to learn how to sell your book, because publishers will NOT invest in new, unknown writers. If you have a network and "platform" for contacts for sales, be sure to include them in your biography and proposal.

It would help if you are a hero, an astronaut, a politician or any other fame-yielding persona. Good luck.

I would say you should read a lot of articles about the publishing world. It's not easy and it can be really tough. You also have to write something that you'd like to publish. So, I would say write your story first, and then start looking into publishing. That way, you don't stress yourself out too much.