Study the competition. To be a successful writer, you need to be familiar with not only what ground has been previously covered but also how it was covered in fresh and innovative ways. For instance, although the romance genre is known to follow a standard formula of "boy meets girl/boy loses girl/boy gets girl back," the broad number of variations employed involve elements such as conflicting religions, the chasm of respective job/social status, and fantasy obstacles such as time travel, science experiments and magic spells.
Identify at least three things in your plot that are unique from the titles you have researched in Step #1. For example, suppose you are an expert on Mesopotamia and have written your romance novel in this time period. Unlike many period romances that transpire in the Middle Ages, during the Civil War, or at turn-of-the-century London or New York, the setting of Mesopotamia is pretty much an untapped territory and readers would probably be interested in learning more about it. Furthermore, your heroine has come to power by pretending to be a man. Thirdly, the object of her affections is blind and wouldn't know how beautiful the heroine was even if she wasn't in disguise. Put these three spins together and you've got yourself a good hook.
Identify at least one thing about yourself that puts you in an expert position to write this book. Let's say that you have written a nonfiction text about how to cope with the challenges of living with an autistic child. If you are a doctor or educational professional whose specialty is the field of autism or if you are a parent who has gone through the experiences of raising an autistic son or daughter, your level of credibility will cause readers in similar circumstances to seek you out for advice and support. Even in a fictional context (i.e., a crime novel), the real-life experiences you can bring to the table (i.e., as a former detective/investigator/attorney) will make the events that transpire in the book resonate with accuracy. This is the kind of supporting documentation that editors notice when you mention them upfront in a query letter.
Summarize your plot in one short question. If, for instance, your book was adapted to a movie and it was playing at the local theater, what would the teaser on the lobby poster say? The question you come up with should be something that not only dares a reader to wonder "what if" but also drops a hint as to what the movie is going to be about. Example: "What if the greatest magician of our time...wasn't from our time?" This technique works well as the opening line to your agent/editor query letter because it dares the recipient to keep reading to find out what it means. Steps 5-8 offer other openers that will keep your submission from sliding into the slush pile.
Compose a controversial statement that catches the reader off guard. Whether it's the first line in your book or the opening line in your query letter, the intent is to grab their attention. If, for example, you noticed a magazine article titled "Your Diet Is Killing You," you'd be drawn to read it because it contradicts your belief that diets are supposed to help you lose extra pounds to live longer.
Open with a fact. If your book is nonfiction, this is pretty easy to do because you're probably just lifting something from one of your own chapters that falls into the "bet you didn't know this" category. If you're pitching a work of fiction, however, the "fact" in question can actually be just a creative perception of one of the characters with absolutely no bearing on reality.
Open your query letter with a catchy quotation, especially one that hasn't been done to death. Internet sources such as Brainy Quote (see Resources) are great for this purpose. If it's a quote that you can twist a bit, even better. Example: "Time wounds all heels."
Start your query letter with a story. It could either be the opening paragraph from the book itself or it could be the synopsis. The latter is especially effective if it's a first-person narrative based on a true event. Example: "Dear Ms. Jones, If someone had told me eight years ago that I'd be writing to you, I wouldn't have believed them. There's nothing about my personality that shouts 'writer' nor anything in my family background that I ever felt was extraordinary. For as long as I can remember, I've simply gotten up every day and gone to work and come back home. All of that changed, though, on a Tuesday morning in September when the world as I knew it came crashing down and I was soon thereafter listed among the missing."
Study the list of the "100 Best Novels of All Time" (see Resources). As time permits, read the opening paragraph of each book for its "hookability." Likewise, read what the critics have said about what made each book stand out.