on Just Publishing Advice:

Author promotion is probably the last thing on a new author’s mind when publishing their first book.
Promoting a book is relatively easy. There are plenty of options for book advertising as well as book promotion services.
A new author also has plenty of alternatives when it comes to using free book marketing ideas and tools and social media.
But promoting a book continuously can often lead to your online contacts becoming ad-blind to your book marketing plan. This is why author promotion can be beneficial.