Over the past five years or so that I've been seriously writing, along with the more than six years I've worked at the company as a proofreader, I've been asked several times how one goes about writing for Harlequin.
Let me preface this by making it clear that I do not speak for the company. This has been gleaned from my own personal experience.
Let's explore, first the reasons you are asking this question.
Why do you want to write for Harlequin? This is a very simple question. If the answer is "because they'll publish anything and I hear I can make easy money writing trashy romances," then stop. Just stop. Writing is not easy, and getting published by the world's largest publisher of women's fiction is even more difficult. Any belief that this will be easy and that you'll become a millionaire overnight needs to be put down right now. (See my About Me page.)
If, on the other hand, the answer is "I want to write for Harlequin because I've got a great idea/completed romance manuscript that would be terrific for their (insert series here) line," then you, my friend, are on the right track.
But what if all you have is a vague idea and a glimmer of hope in your eyes? How do you sell your book to Harlequin?
1. If you want to write for Harlequin, read Harlequin books. Two or three is not a sampling. Ten is not a sampling. I daresay, 100 probably isn't a sampling, either, but it's closer to some kind of representation (as of this date, I have read more than 670 Harlequin books over +6 years). Harlequin produces tons of different series ranging from contemporary to paranormal. Go to Harlequin.com and study the enormous range of series they have. Understanding what you like and where your story will fit within the Harlequin family is vital.
2a. Write, write, WRITE. Don't just sit and plan and outline and dream. You have to have words to edit before you even consider who you'll sell to or what agent you want. The only way you'll become a published author is to write. Period. A book is not going to magically appear in your hands. Finish writing a book and you'll be that much closer to being a published author.
2b. Edit, edit, EDIT. Your manuscript should be the best it can possibly be. Polish it to a high gloss before you start handing it out...and expect to edit it some more even after you've sold it!
3. Get help. Learn about the romance publishing industry. There are tons of resources out there for the would-be Harlequin author to help you sharpen your writing and learn about the publishing business. The Harlequin website has an entire online community devoted to the craft of writing.
Another resource: The Romance Writers of America is the primary nonprofit organization created to foster the careers of aspiring and published romance authors, and it can give you lots of great perspective about the industry overall.
Go to your local RWA chapter meetings. Find a critique partner or critique group of like-minded writers who work in your genre. And unless she's a book editor, your mom probably doesn't count. Listen to what people have to say about your writing. Seek out resources on the internet and in books. You can never learn enough.
4. Submit your manuscript for consideration. You can't get published by Harlequin unless you stick your neck out there and submit. Check out the submission guidelines on the Harlequin website and, for the love of all that is holy, FOLLOW THOSE GUIDELINES. Nothing will get you rejected faster than flaunting the rules...except maybe dissing the line you want to write for in your query letter. (Note: Don't do that.)
5. Accept rejection. It'll happen. But don't let it discourage you! Learn from your rejection letters. Go back to step 3. Edit.
6. Repeat steps 1-5 until you are published by Harlequin. Writing to get published is not easy. I don't know how often I have to say this. I have 5 books I completed that are sitting on my hard drive, rejected or unpublishable. I've learned from every one of them. And though they'll never see the light of day, at least I can say I wrote those books.
For more tips (helpful or otherwise) check out my So You Want To Be A Writer page for all my posts on the craft and on getting published.