Before you send your Query Letter, you need to find the right Literary Agents.
Once your book is absolutely the best it can be, you need to find literary agents who specialize in your genre. There are several websites and books that it can help with this (Publishers Marketplace, Writer’s Market, the Guide to Literary Agents, Jeff Herman’s Guide, plus many more—check your local library!).
Do not send your query to an agent who does not specialize in your genre—even if you’ve heard great things about that agent. Why not? Because the agent will stop reading your letter the moment he/she (note: I will use “she” from now on) determines that it isn’t in her specialty area (genres). More importantly, the agents will ignore you because they can’t help you. Agents know their genres inside and out, but they don’t know every genre. They, like you, probably don’t like every genre. Agents are people with particular tastes. In addition, agents develop relationships with certain editors. Editors, like the agents themselves, have niches. Agents will often represent several genres, but no agent represents all genres. An agent who specializes in mystery may not be able to sell romance because the agent may not know anything about romance or have any connections with romance editors—so don’t waste your time or theirs by writing to them. The only possible case when you might send your query to an agent who does not rep. your genre is if you have a personal connection with that agent. In that case, maybe the agent will do you a favor and recommend your book to another agent who can help you.
You will need to do a lot of research. Start with the above books and websites, but search the internet. Once you’ve found an agent who might be interested in your novel, go online and find out as much about that agent as you can. Google her. If she is on Twitter, follow her. You can learn A LOT about people on Twitter including what they really want, their pet peeves, likes VS dislikes, etc. Also search for interviews with the agent, see if the agent has a blog or website, etc. Once you know your audience, you’re ready to write the rest of your query (the paragraphs about your novel will probably stay the same—see my post about “Query Writing Tips Part 1 – Your Novel”).
Check the agent’s website/agency website to find exactly how she wants to receive queries. Do not deviate. At this stage, they are looking for any excuse not to read your book (even though they want to find a great book). If you can’t follow directions, you won’t get read.