I never set out to become an author. My main source of income had always been through my work as a psychotherapist. I'd only started writing articles as a way to earn extra money after my husband passed away.

But everything changed when one of my articles--13 Things Mentally Strong People Don't Do--went viral. Millions of people read it and within a few days, a literary agent contacted me and suggested I write a book.

I knew nothing about the publishing industry. But I knew I wanted to do it.

I spent the next couple of weeks creating my book proposal (after I researched how to write one). And incredibly, that proposal landed me a deal with HarperCollins.

I spent the next few months writing, editing, and rewriting. And just 13 months after my article went viral, 13 Things Mentally Strong People Don't Do, went on sale. Remarkably, it hit several bestseller lists and was even named one of the best business books of the year.

As an accidental author, I'm humbled and grateful I had the opportunity to write a book. From invitations for international speaking engagements, to producing my own eCourse, a traditionally published book opened up a lot of new opportunities for me. Not to mention, it's a pretty surreal experience to see my book on the bookstore shelves!

If you hope to land a nonfiction book deal with a mainstream publisher, here are seven things you'll need to be successful:

1. A Fresh Idea

To capture the attention of an agent and a publisher, you'll need a captivating idea. It could be something completely original or a fresh angle on an old idea. Publishers will want to see what will set your book apart from the rest.

2. An Engaged Platform

It's not enough to have a great idea--you also need proof that people are interested in your idea. If you only have 100 social media followers and a dozen blog readers, you'll want to grow your platform to prove people want to hear your message. Show prospective publishers you already have an audience who is eager to hear more.

3. Expertise

Have you studied the subject of your book for decades? Are you viewed as a credible leader on the topic? Be prepared to explain why you're the best person to write--and promote--the book.

4. A Motivated Agent

You can't pitch your ideas to most mainstream publishers directly--they only take proposals from established agents. So, you'll need to find an agent who believes in you and your ideas. Your agent will help negotiate a fair contract with a publisher, which is worth every penny of their commission.

5. A Killer Proposal

Publishers buy books based on proposals, so no need to write the entire manuscript up front. A nonfiction proposal includes components such as a table of contents, chapter summaries, and a sample chapter or two. It should also include a clear business plan that shows how you'll help sell books.

6. A Winning Marketing Strategy

As someone once said to me, "It's called the bestseller's list, not the best writer's list." The decline of brick and mortar bookstores and the rise in the volume of books being written, means selling books is really hard work.

Although a publisher will help provide you with marketing support, much of the promotion is your responsibility. Whether you do speaking engagements, or you write for a major publication, you'll need to find ways to attract attention for your book.

7. A Clear Writing Plan

If you get a book deal, take time to celebrate--but don't celebrate too long. Your book isn't going to write itself (unless you hire a ghostwriter). Researching, writing, and editing take a lot of time.

Create a clear plan for how you're going to carve out time to complete your manuscript. Whether you write a little each day or you set aside a couple of days each week to focus solely on your book, create a schedule and a timeline.

But stay flexible. The best ideas may come to you when you're standing in line at the grocery store or when you're in the shower. Keep a pen and paper handy so you can jot down your ideas whenever inspiration strikes.