If you want to write nonfiction you must first determine your writing goals. Narrowing your goals to fit into a niche will help you define where you want to go as a writer. The more narrow focus you can achieve, the better your chances for success. For example, you have experience in business management. That's a broad category.

Consider:
Who is your audience?

Let's say that you decided that you would like to write a book to help new business managers. You want to share your knowledge with them. That's still too broad. Now consider:
What are your strengths?
What specific skills are you knowledgeable about?
What is the specific area of business management at which you excell?

After thinking about these questions, you determine that your strengths are that you easily connect with people and have been praised for your training abilities. Upper management has recognized your talents as a trainer. Now you can narrow your writing niche to training and decide to write a book about effective training practices. 

Now, before you begin writing your book, do your research and check out other books on training that have already been published.

Answer this critical question:
How can you write from a different perspective that will make your book stand apart from all the other books on the market?

Narrowing your niche and doing your research will give you a clear focus and make the writing process more enjoyable.