Sign up for an Amazon Associates account and place a link on your own website utilizing your linking references from Amazon.. In many cases the commission you earn from Amazon can be more than the royalty you get from your publisher, and you’ll still earn that royalty.
Explain clearly that if they are interested in buying your book, you’ll earn an extra commission if people click the link on your page, go to Amazon, and immediately add your book to their cart. You may want to explain that you WON’T get the commission if they simply go to Amazon without clicking YOUR link, or if they click on the click, then go elsewhere within Amazon before adding your book to their shopping cart. If it doesn’t cost them anything extra, many people are happy to help you earn extra dollars for the sale.