The first step--and of course, the most difficult--is to actually write a novel that others might be interested in reading -- to say nothing of all of the reviews / rewrites / edits required to bring the manuscript up to publication quality.
Next comes the query letter--which is a tool used to "hook" the interest of agents. Writing an effective query letter is also quite difficult, as it requires you to summarize the entire plot of your book into two engaging paragraphs [a much harder task than it sounds] that will either pique the agent's interest to read more or induce them to file your query in the round filing cabinet beside their desk.
From there, the hopeful author has to cast themselves upon the fickle winds of agent opinion... and be prepared for lots of rejection. The querying process is a lot like applying for jobs on the internet or via classified ads: your percentage of getting a positive result is exceedingly low. What ensues is a confidence-crushing cascade of impersonal form rejection letters. Even famous authors aren't immune, as evidenced by this list describing agents' negative reactions to books that eventually went on to become literary classics.
But if the author believes in the project and isn't deterred by a few rejections--and of course, if the quality of the manuscript makes the novel worthy of publication--once in awhile you'll get a few gratifying nibbles:
Dear Mr. Falcone:
Thank you for sending me sample pages of your novel. I would like to take a look at the entire manuscript.
Thank you for your query. I'd love to read the first three chapters of...
...and suddenly all of the hard work you've put in is worth the effort you've expended and disappointment you've faced getting to that point.
I want to be clear: landing an agent is only the first hurdle a writer must overcome on the arduous path to getting a novel published. But positive reactions from agents like those listed above only make me more eager to see my first novel in print. I look forward to the day when I can walk into a random Barnes & Noble and see my book upon the shelves!
Thanks to a few visionary agents, I'm more confident than ever that it'll happen.