Publishers spend big, big dollars on certain books—and they're careful about which ones. They often engage outside PR firms, place ads in magazines and occasionally on TV (which is far more expensive). They target the books they believe will sell. Their marketing people set up interviews on the big, prime-time shows.
Until she left her daytime show, almost every author promoted by Oprah hit the best-seller lists. Today, Good Morning America, and a few others still do well—but no one has yet become the doyenne of making best sellers.
Sometimes publishers also cross-promote. If they have a book with a similar theme or within a particular genre, they'll add a page, usually in the back of the book, that says or implies, "If you liked this book, you'll also like . . ."
If you're a newer author, forget about big-budget promotion—unless your publisher says, "This one stands out—way, way out."
Another factor about publisher promotion is that once a book begins to sell big, the publisher gets behind it. Baker Books spent a lot of money promoting 90 Minutes in Heaven—but only after Don Piper went out on the road and made the book into a big seller. That was wise of them. They saw the potential, so why wouldn't they put their money on 90 Minutes in Heaven instead of a book that might sell only 20,000 copies?