1. Read books.
When you love one, turn to the acknowledgements and see whom the author has thanked. One of those people will certainly be their agent. If you feel like your own work is in line with this book you loved, chances are the agent who represented it will be a good fit for you. (Added bonus: reading more makes you a better writer!)
2. Look at Agency websites.
Are there any agencies you respect, or have at least heard of? If so, find their websites. Chances are there will be an “about” or “agents” page where you can read about the different agents working there. Each agent will describe what they’re looking to represent and if your work fits the bill, query them! (Added bonus: this is a good way to find the junior agents who are just starting out.)
3. Be on Twitter.
Having a Twitter is great, and it’s a productive way to be engaged with the publishing world. Follow agents and editors and learn more about their tastes through their posts. Chances are they’ll talk about their slush piles and what they think is missing from their lists. Don’t be creepy about it, but interact! That’s what we’re on Twitter for. A lot of agencies host #askagent talks where they’ll answer your questions. Ours uses the tag #askinkwell! (Added bonus: the more you interact, the more followers you’ll get, the better your author platform will be!)
This seems obvious, but in this day and age, almost everything you could want to know about an agent is somewhere on the internet. Google people you’re interested in working with! Maybe they have a blog, or an interview with them has been published in Slate or Poets & Writers. You can draw from this information to better guess if you and the agent in question would work well together. (Added bonus: thorough researching can really improve your query letter.)
If you know anyone who is a writer or who works in publishing, chances are they have opinions about how to best find an agent. They might even know someone who IS an agent! Approach them and ask for their advice. Recommendations and help are always more meaningful coming from people you might actually know. (Added bonus: networking is helpful even if you don’t already know writers or people in publishing. Go to some readings, follow and comment on some blogs, and write fan letters to writers you admire.)