Just kidding. I really don't know. Here are some thoughts, though.
First they have to know it exists. Estimates vary, but there are thousands of books released each year. Just having someone hear your title is a plus, so you need to let people know that there is a book. A lot of people.
Second, potential readers have to become intrigued. I've worked on this one, because I tend to be a real self-deprecating sort and, the first time a friend told me he wanted to read my book, found myself replying, "Oh, you don't have to read it." STOP THAT!" I told myself later. The author should not talk the reader out of taking a look. The reader will decide if he wants to read it/finish it/buy the next one. Not my place to judge. What I've tried to do is come up with a soft pitch that gives the basics in a conversational way, so I don't sound like a movie trailer but I do get the essentials across.
Third, each reader has to decide if the book is worth buying. That's a hard one, since my book is in hardcover and people tend to cringe when they see the price. I can almost see it float through their heads, "I MIGHT pay this much for a Harry Potter, but who knows if Peg can really write?" Again, only the buyer can decide, and I shouldn't (hopefully won't) be offended if some people choose to borrow it from the local library instead. In fact I hope that a lot of people call their local libraries and request the book. Then the libraries will buy it, and they're used to paying hardcover prices.
I do know how I won't be marketing. I will not shove the book into someone's hands and say, "You're going to love this." I will not follow people around in bookstores and ask irritating questions. It garners sales for some authors; I've seen it happen. But I wonder how many people who are schmoozed into buying a book are disappointed when the book doesn't live up to the hype. Those people will never buy that author's work again. I've had it happen to me and later asked myself, "Why did I let that guy talk me into this junk?"
I guess what I'm saying is that for me, MAKING someone buy the book is different than making them WANT to buy the book. I can't guarantee that you'll love my novel. I can only guarantee that I loved writing it, and that shows in the finished product.