First week sales numbers determine many factors: how much more publicity money the publisher will free up to promote the book; whether they will continue to employ a writer or set him loose; and, if they do keep the writer, how much his or her next advance will be. Most authors will only make a best seller's hit in the opening week. The majority of books do not have long-term sustainability. Only a fraction of all the books ever published remain in print years after they come out.
1. Pre-order the book. Whether on line or at a reporting store, all pre-orders count toward first day of sales, and ultimately, that week's final tally.
2. Use a reporting store. Not all book stores report to the New York Times, which uses its numbers to determine its rankings list. The New York Time Book Review is the premiere list all authors want to be on.
3. If you forgot to pre-order, or your paycheck doesn't come in until the Friday after the book debut, no problem. Books in the U.S. drop on Tuesdays. As long as you purchase it by Sunday night, it still counts as first week's sales. The book lists are measured in weeks.
So how can you tell if a bookstore is a reporting store?
1. Look at their events schedule. If they are booking Stephen King, Tom Clancy, Amy Schumer, Hilary Clinton, George R.R. Martin, or other top authors to sign books, then they are very likely a reporting store. And with chains like Barnes & Noble, only a select few fall into the NY Times reporting category.
2. Amazon.com and B&N.com are also reporting stores, so buying on line helps.
You bet it does. Your author may not make the top 20 of the main best seller's list, but there are also genre lists for fantasy, science fiction, romance, westerns, non-fiction, and more. Books that don't make the main list can still score on the genre list. Maybe it's number 346 on the main list, which includes non-fiction, but it's number 21 on the mystery list. That's still a big help to the writer and the people promoting his/her book.
So help your favorite author out when you can. The more they can show their publishers their success, the more likely they are to continue writing your favorite stories, and not have to resort to teaching or taking a corporate job, which will delay their next story from reaching you. Ninety nine percent of writers are not millionaires. The John Grishams of the world are the exception, not the rule.