The greatest opening to any book is found in Cannery Row by John Steinbeck. It goes:
Cannery Row in Monterey in California is a poem, a stink, a grating noise, a quality of light, a tone, a habit, a nostalgia, a dream. Cannery Row is the gathered and scattered, tin and iron and rust and splintered wood, chipped pavement and weedy lots and junk heaps, sardine canneries of corrugated iron, honky tonks, restaurants and whore houses, and little crowded groceries, and laboratories and flophouses. Its inhabitant are, as the man once said, "whores, pimps, gambler and sons of bitches," by which he meant Everybody. Had the man looked through another peephole he might have said, "Saints and angels and martyrs and holymen" and he would have meant the same thing.”
To say that this is the best of all opening paragraphs ever is not really a controversial thing to say. Many people agree with this statement.
However, the point I want to make is that writers need to think about how they draw the reader into their book. In one paragraph, the reader wants to keep going, wants to find out if the writer can live up to the promise of this opening.
Look also at the opening five pages or so of The World According to Garp by John Irving. Again, good storytelling creates a strong opening promise to the reader that is you stick with me, I'll at least entertain you.
Then look at the opening fifty pages or so of The Story of Edgar Sawtelle. This book did very well, but only because readers were willing to get through those first fifty pages.
Now, think of every book you have ever loved and think about how long it took to hook you in. My guess is that you fell in love within the first few pages if not the first few words.
Make it easy for the reader to fall in love with your book. Spend time crafting an opening that makes a big promise.