I've realized what it takes for me to buy a book by an author I've never read before, and I call it Three Good Things. Here's how it worked the other day:
Step 1: I went to the bookstore.
Step 2: I took my sons to the trains in the back and had my husband watch them so I could browse.
Step 3: I went over to the Young Adult shelves and started looking. When I noticed an interesting title, name, or cover, I'd pick up the book.
Step 4: Once I have the book in my hands, I examine a few things: the cover art, the summary inside the jacket, the author bio/dedication, blurbs, and, if at least two of those things impress me enough, the first ten to twenty pages (I tend to read more than most people might because A) I'm a fast reader, B) I love slow-starting books like Gilead and Middlemarch, and C) I have empathy for other authors). If I love the pages, I buy the book.
Obviously a lot comes down to the pages, but a lot goes in to getting me to read those pages. A friend's recommendation is huge. So is author recognition (when I know the author from novels I've heard of/grad school/book lists). But the title and cover art and back summary and author bio all matter, too. And if I see something I don't like in any of those sections, I put the book back on the shelf. Like a book I won't mention by name except to say it has "Witches" in the title--I like witches, so I picked up the book. The cover was okay, and the introduction on the fairy tale elements had me interested. But when I read the author bio, and saw the author really liked New Age stuff like crystal therapy and soy, I decided I'd only give it five or six pages instead of my regular twenty. Within four pages, I knew I didn't want the book. I might pick it up at the library, if it's available, but I've found that it takes three things for me to buy a book (plus pages), and only two things for me to pass.
There were two books I recently purchased based solely off the three-point rule, although I didn't realize it consciously. The first time it was Sunshine, by Robin McKinley.
More recently I wanted to see what made for a good summary, and I found the book Wither:
So there you have it. What makes me buy a book by an author I've never heard of (a hardcover, no less!). I'm sure I'll buy more debut books as I get back my teaching income in September (and/or if I sell my own book!), but right now I'll still visit the bookstore and trail my hands along the covers and read the summaries and author bios and blurbs and, if I get at least two points, or one point that's super good, those crucial first pages...