Where highlighted, enter in your best keywords, and your individual book ASIN #.
Now test the link to make sure your book shows up first on the page. If you use just one target keyword, you DO NOT need the + sign. This is only for multiple keywords.
What this code can do is amazing. Any time you advertise your book, use this code. This tricks the system into thinking that the person who clicked on your link, specifically typed in the specific search terms/keywords, linking your book to the keywords of your choice.
This will improve ranking and place your book on the front page for the search terms. Even if the person does not purchase your book through this link, the clicks alone are worth the effort.