You’ve got to make connections with booksellers early
I was reading a post on a Sisters in Crime group by a bookstore owner. He advised contacting bookstore owners and offering a free copy of your book, and then said, “But if you're waiting for when the book is out, you're really behind the curve. You want to get to booksellers with signed ARCs, tied to when booksellers are placing orders for the season. For an April St. Martin's title, that's part of the January through April catalog. We met with our St. Martin's sales rep and bought for this season back on October 9, according to my calendar. So that's when the real work of evaluating titles is happening, when you have a chance to influence how many copies are being ordered. If you wait 'til later, you're relying on overworked booksellers and sales reps to make adjustments to orders placed in the past -- sometimes that's asking a lot, even for well-intentioned booksellers."
[Note to self: make sure have ARCs of new book in booksellers’ hands six months in advance!]