Q. What makes readers decide to buy books, and how can I get them to buy more of mine?
A. The simple but nontrivial answer: in the vast majority of cases, people buy books because they think they're going to enjoy reading them. Don't dismiss this as obvious, because everything flows from it.
The single most important reason someone decides to buy a book is because they've read and enjoyed another book by the same author.
The second most important reason (and it's a big step down) is because the book was recommended to them by someone or something they trust.
The third most important reason (another big step down) is because they liked the cover. Usually this means the cover illustration was attractive, and made the book look like the sort of thing they enjoy reading.
All other reasons are trivial by comparison. This includes advertising. Think about it: why do you buy books? Odds are, you do it for the reasons I've just described. People have wildly diverse tastes in reading material, but they have a small number of reliable strategies for finding it.
How can you get readers to decide to buy your offerings? For starters, write a good book. There's no substitute for that, because no one can make readers buy and read a book they don't want. Massive amounts of promo and advertising certainly won't do it, as the publishing industry can tell you from experience.
Beyond that? Everything publishers put into packaging books -- cover illustration, cover design, type design, quotes, blurbs, sell lines, story copy, author bio, etc. -- is there to help readers figure out whether this is a book they'll enjoy. If they don't know anything about the author, it's doubly important to bridge the gap between book and reader. If you're self-publishing, do your best to duplicate that effect.
Don't neglect the online booksellers. This is especially important if your publisher doesn't have a distribution deal that routinely gets their titles onto bookstore shelves. Check out the online listings for a well-published and popular book or author. Notice the good-quality cover image, the descriptive copy, the quotes from professional review sources, and all the other details? They're there to help sell the book. If your publisher hasn't provided some or all of those, get in touch with the retailer and see if you can provide them yourself.
Set a cutoff date for full-scale promotion efforts on behalf of your most recent work. When you reach it, knock off the promo and start work on your next project. You didn't become a writer in order to spend your life doing PR. Go back to your writing. Every good book you write is an advertisement for every other book in your publication list. Every reader who enjoys one work of yours is part of the audience for your other work.
Next: to quote Neil Gaiman, "Never publish anything bad." That's a self-inflicted wound. A reader who's enjoyed your writing so far, then gets hold of a piece of yours that's noticeably weak or awkward, will never trust you quite as much again.
In general, try not to lie about anything. Being able to lie well and convincingly is a high-end professional skill. Odds are you don't have it, so best not do it at all.