The power of a query letter cannot be overestimated. An agent forms a first impression of you and your manuscript from your query letter, and it's often solely responsible for convincing the agent to read your work.

There's no true formula for a query letter; if there were, every single manuscript would be requested by every single agent.  Instead, I'm happy to share the advice I give to my clients, based on more than a decade of reading queries as both an acquiring editor and a first reader for literary agents.

I usually recommend that you start with a personal note to the agent that includes the word count, genre, and title of your book, followed by one to two paragraphs describing your story, a couple of sentences of your biography, and then a closing paragraph thanking her for her time and conveying that the complete manuscript is available upon request. Here are a few more tips:

1. Do your research on agents.

Nothing's going to get your query letter deleted from agents' in-boxes faster than approaching them with something they've never sold and never will. Your adult Civil War-era novel is unlikely to appeal to an agent who's been selling only modern-day young adult fiction. It's a waste of everyone's time, so before you start submitting your query letter, come up with a targeted list of appropriate agents who deal with books in your genre.

2. Personalize.

Agents like to know you've done your research, because it shows them what type of career author you'll be. Plus, it's nice for them to know you actually looked into them and are courting them personally, instead of just going down a list and sending the same form letter to everyone. Let agents know why you're approaching their particular office. Did a book by one of their clients change your life? Do you follow them on Twitter, or did you read their blog and a particular piece of advice stood out? Be sure to make this genuine and specific, and if you don't have something nice to say, then say nothing at all.

3. Write a description of your book that lets an agent know exactly what she'll be reading.

Describing your manuscript in the one or two short paragraphs that a query letter usually allows is one of the hardest parts of the query letter process. Think of the story copy as a succinct and dynamic abbreviated synopsis. I tell my clients to go to bookstores and look at the back-cover copy of published novels. Those sell books in exactly the same way you need to sell yours, and they let readers know exactly what they're going to be getting if they buy the book.

4. Sell yourself.

Make it personal, but keep it relevant. An agent doesn't need to know where you went to college or what you majored in unless it's directly relevant to the book you're trying to sell. An agent will want to know if you have any writing credits (unpublished manuscripts don't count, and I probably wouldn't mention any self-published books unless something truly major happened with them). Tell the agent if you have some kind of amazing platform, like 15,000 Twitter followers or a highly read blog.

5. Ask someone who's never read your manuscript to review your query letter for you.

Coming in blind--with no knowledge of what your manuscript is about and with no preconceived notions--is exactly how an agent will approach your query. As the author of the manuscript you're trying to sell, your mind will often fill in blanks, so it's almost impossible to tell what information you're missing. It takes a fresh pair of eyes to point out what's missing.

Once you feel your query letter is as perfect as you can make it, it is time to start the querying process. I recommend sending out 5-7 queries every few weeks, so you have a chance to gauge how your query letter--and manuscript if an agent requests it--is working for you. If you receive any constructive feedback--or your query is met with resounding silence--you'll have a chance to make changes before trying any other names on your agent wish list.

Happy querying!