It's never too early to start marketing your book.
Never use the phrase: 'buy my book' - ever.
At Brandies I discovered Feminism. And I instantly became a convert... writing brilliant papers in my Myths of Patriarchy class, in which I likened my fate as a woman to other victims throughout the ages.
Marketing starts even before our books are published.
Book marketing should be a planned process, an art if you will.
Book marketing is a skill: it takes knowledge, effort, and persistence to really be successful.