With one book, you can build a six-figure business that pays you year in and year out, even if you never write another book again.
Your book can be a physical book, ebook or even an audio book.
Frankly I recommend you start with an ebook so that you can instantly send it to anyone you choose and not have to bother with mailing a physical copy.

Noah Kagan of AppSumo is known for starting several companies and growing them to 7 or 8 figures in revenue.
Recently, while participating in a 24-hour business challenge to prove that anyone can start a business today, Noah asked his followers what business he should start.

Ten or fifteen years ago the ‘get rich’ advice usually included making apps. Remember hearing things like this? “Make an app, sell a million copies for 99 cents each, and you’re practically a millionaire!”

Here’s a super simple method to:
Increase the apparent value of your product
Place your product among the very best in the business
Make your product an instant mainstay by association

This is, pure and simple, a lesson in flexibility and adaptation.
All too often I see new marketers who KNOW what their customers want and KNOW how to best market that product to them.
And these are almost always the marketers who fall flat on their face because no one can tell them anything different – not even their customers.