Supposing you’ve followed the first three steps, writing a brilliant novel, obtaining feedback and revising according to that feedback, you should now be ready to query. Simply put, a query is a short letter, no more than 500 words, that makes an agent want to read your manuscript. Like anything in the writing business, there’s a whole list of rules for query writing. These rules can occasionally be broken, but unless you’re absolutely brilliant, following the format is by far the best way to snag an agent.
Firstly, you’ll need to find agents. Agentquery is a great place, and you can search by genre and whether or not they’re open to queries at the time. It’s also a good idea to look in books that you liked and read the acknowledgements. The author will almost always thank their agent. It’s always good to mention in your query that you’ve read and enjoyed other books the agent has represented.
Then you need to get to know the agent. Do you actually want this agent representing you? An author/agent partnership will affect the rest of your career, so chose wisely. Look at the sort of books the agent sells. I want an agent with tastes similar to mine, so I wouldn’t pick one who sells a lot of paranormal romance or erotica. As an unpublished author, it sometimes feels like just getting any agent would be amazing, but honestly, no agent is better than a bad agent.
Once you have a list of agents you would like representing you, you need to send out your query. I’m not going to tell you how to write a query; Nathan Bransford, Query Shark and Elana Johnson can teach you that much better than I can. Once you have the query, send it out to a couple agents, perhaps ten at a time. Make sure you follow the individual agent’s guidelines. Some will just want a query, others will want the first couple pages of manuscript and a synopsis (though it's almost always a good idea to paste the first chapter or two in the email unless the agent specifically requests that you don't. Agents always like to get a feel for your writing style. But whatever you do, DON'T send an attachment!). Always address your query to the agent by name; nothing kills a query faster than ‘Dear Mister/Madam.’ These may seem like little things, but your first impression is so important.
And then… prepare for rejections, because you will get them. I’ve only heard of one author who got their agent first time. Everyone else had to go through many, many rejections. Leigh Fallon, the first inkpopper to get published by HarperTeen, didn’t get an agent the first time around. Don’t respond to the rejections; just delete them or store them away somewhere, and move on.
At last, at some point, you should hopefully get a request for a partial or full. You’ll send this off to the agent formatted as they request, and then prepare for another rejection. If you’re amazingly lucky, this is where you get an offer of representation. The agent will call, you’ll talk, and if you think this agent would be a good fit for you… Ta da! You’ve got an agent!