1. Address the agent formally by their last name: Mr. or Ms. Smith followed by a colon. You may address them by their first name if you have a relationship with that agent or the agent addresses you by your first name.
2. Remember your query letter is a business letter. Use spell checker, be concise, don’t ramble on about your story or yourself, don’t put yourself in a negative light (listing how many times you’ve been rejected), don’t use flowery fonts, do be respectful. Nathan Bransford's How to format a query letter
3. Follow the agent’s guidelines. If they want the query and X number of pages pasted in the email, don’t send attachments and vice versa.
4. Read their profiles to see what they represent. Don’t send genres they’re not interested in. You are wasting your time and theirs.
5. Don’t get cute or clever with the query letter. One writer turned the query letter into a question and answer format about the writer. The end result was the query letter was all about the writer and very little about the writing project.
6. Do try and highlight your writing voice in your query letter. This can be accomplished by taking text from the manuscript and using it in the letter. Text that is funny, witty or a clever turn of phrase gives the agent a taste of your writing style and hints about the story.
7. After you make your submission, do not call or email the agent pestering them if they received it, did they read it or when will they read it. Believe it or not, reading their slush pile is not their primary job.
8. Be respectful of their time. Their primary job is taking care of their current clients including tracking down royalty payments, getting submission packages ready for editors they want to query, reading manuscripts and making revision notes for current clients, negotiating deals with editors over current submissions and negotiating contracts once an offer had been accepted to name a few of their jobs.
9. When you receive a rejection letter, do not contact the agent complaining that they didn’t tell you why the manuscript was rejected it or how to make it better.
10. If you receive a detailed revision request from an agent (multiple pages with thoughts, comments or suggestions on how to make the manuscript stronger/more marketable), you owe that agent first look.
11. Know the acceptable word counts for your story. Don’t send a 2000-word picture book or an 80,000-word chapter book or middle grade. This is an instant rejection. You can find word counts online.
12. Pick a lane. Don’t write your story, intentionally or unintentionally, so it straddles the line between middle grade and YA. There are important distinctions between a middle grade story and a YA. Writer's Digest Key differences between middle grade and young adult
13. Always be courteous and considerate of the agent’s time. Never insult, threaten, berate or belittle the agent. Being rude never works in your favor and agents do talk to each other.