A book is not a stationary thing if you don't want it to be.
In fact a good book can become a sales machine.
Aside from affiliate programs and selling your own products you can also use your book to promote your events.
The type of events that you can promote can maybe be a convention that your company hosts every year or you may run a business that criss crosses around the country just doing speaking engagements or if that's not your thing you can also promote live webinar events that you can do from the comfort of your home or office at your own pace.
Now if you don't have an event planned or had not even considered that before you still have something you can do.
Start sending your readers to a page so that they can sign up for email notifications for future events that you are hosting.
So now you know for a fact that you have people who are still interested in hearing what you have to say and now you just created an opportunity to sell to them over and over again.
Now people aren't going to give you their name freely in the expectation that maybe, someday you might be doing a presentation.
Give them some incentive.
Maybe write up a quick report that goes more in depth on a certain aspect of your book, or offer an MP3 of an interview you have done or a webinar that you have done in the past.
Just give them something that offers them some real value.
Then after that you will be able to promote your events to your list of people and create a core group of buyers every time.