1. Go to the bookstore.
2. Find books like your book.
3. Check the acknowledgements and the author’s website to identify their house, editors and agent.
4. Now you have some idea where to submit and a nice opening to your query letter. “I’m submitting to you because your association with of X’s excellent book…”
5. Check the agent’s website and make sure you confine yourself to their requested parameters for submissions.
Try to get a sense from their voice on their site. Does this person sound like someone you could marry? Yes. It’s that serious.