In most cases, if you want to land a writing agent you need to write a query letter.
So, while there are a few differing opinions on how to do this, the consensus is that it should be no more than around 300 words and definitely no longer than one page. Below I have pasted a couple of links to good sites concerning query letters.
I have referenced these sites an innumerable amount of times, and the one that seems closer to the industry standard is AgentQuery.com. QueryShark is amazing, but she has very specific standards on how she thinks a query should be laid out, and it may be a bit overbearing.
I also got a lot of help from my editor. Below I have pasted her suggestions for query layout and important information to include.
This is a single sentence to a couple sentences in length, and this contains your hook, that phrase that, well, hooks readers. This is the most important point of your query, because it might mean the difference between an instant rejection and receiving a partial/full MS request.
This should lay the foundation of the story. It should introduce the premise, the important characters and the initial conflict. You’ll want to build a strong foundation. I’ve read many weak foundational paragraphs, and the story becomes confusing by the following paragraph.
You are continuing to introduce the elements of your story, but think of this more as the middle section of your story. Make sure to add any exciting information or plot twists—this paragraph can otherwise be boring.
This is where you approach your story’s climax (but don’t give it away).
Now that you’ve gotten the body of your query written, it’s important to go to each agent’s website in order to see what they prefer in addition to what you’ve already done. Some agents like to get the first three chapters. Some want a bio. Some want a synopsis (which is a whole different and awful beast). Some want all three.
Some also have specific guidelines on how they want to receive a query letter. Some only except digital submissions, while others accept only by snail mail. Make sure you know what your agent wants or else it’ll be an instant rejection.
Also, you’ll want to confirm your agent’s genre … it would be an epic mistake and waste of time to query someone who doesn’t represent the type of book you’ve written.
When I was going through this process I was a bit overwhelmed. It felt like I was doing something special for every agent I queried, and I only queried thirty. I did get one request to see pages, but then a rejection. If you’ve read my previous posts you know already that there were major flaws in my masterpiece, so I don’t blame anyone but myself for the thirty rejections that I eventually received.
But it’s important to keep your head up. If you’re lucky you may get some feedback on why you were rejected, otherwise you’ll need to rely on your own judgement (and that of an editor) as to why no one wants your book.
*Other options lay out there though, self publishing is booming! But that’s the stuff of another post.