Complex sentence: Little, Brown, and Company heavily promoted the book and it became the first debut novel to land at number one on the "The New York Times" bestseller list and as of 2005 was the fastest-selling hardback debut novel in US history.
Split into simpler sentences: Little, Brown, and Company heavily promoted the book and it became the first debut novel to become number one on the "The New York Times" bestseller list. As of 2005, it was the fastest-selling hardback debut novel in US history.