I've read a number of generally bad books and I think the one significant benefit all this wasted reading time is that I've acquired a sense of which books will be edifying and well-written and which will be crocks of inscrutable nonsense simply by investigating their covers and backsides. It's not to much of a difficult art, many of these patterns I'm sure you've noticed intuitively before, but it's always nice to have them straightly and outrightly enumerated. So I've complied a list of metrics I use to evaluate whether or not books are even worth the time of day in random order below. Note that most of these rules cover mostly non-fiction, but anything is fair ground.
PhDs on the Cover - When you're reading a book written by a well-repute professional in nearly any field, chances are that they hold a doctorate; this goes without saying. Nonetheless, you'll nearly never see them parading their PhD on the front page; writers who do this typically are simply evoking their education as an appeal to authority and more often that not, may have PhDs in something entirely irrelevant to that they may be writing about. A lot of the literature in pseudoscience consists of dentists writing flowering endorsements of creationism or theologists writing new-age drivel about quantum physics.
Gigantic Author Surnames - This one is actually far more common in fiction, but can be realized everywhere. When I was a kid, I used to wonder why so many books were named "Koontz" in the library; as it ends up, Koontz is just a guy who thinks his last name is far more important that the actual name of his books which grovel somewhere in the corner of the cover. This is essentially of the same substance as flashy PhDs: it's an appeal to authority which distracts from content.
Front Page Cameos - But at least Koontz doesn't plaster his visage all over his books; otherwise library aisles would be more like photo galleries for the self absorbed. Covers are there to expose the passer-by briefly to the content and quality of the book, and people who do think that the most important thing that could sum up their book is their own dim, empty, smiling faces usually are incredibly right. This is most common in the most exploitative self-help guides and any book based on a television or celebrity. In addition to that, this rule will safely steer you away from any pop-politics manuals; honestly, did Bill O'Reilly really think he'd sell more books with his face in plain sight?
Appeals Against Authority - Any book that promises to tell you "what the mainstream media/pharmaceutical companies/your doctor/the system/ doesn't want you to know" is garbage. Anything contained therein is either purposefully controversial nonsense or noncontroversial fact and strawmen presented as such. These should only really appeal to people who believe that there are Masonic super-entities that can so completely control every aspect of your life such that you never find out that fluoride controls your thoughts (just as a note in case, it doesn't). This rule also applies to
Scientific Breakthrus - In case lay-people really don't know, scientists and researchers of all stripes don't write books to be sold in Barnes & Noble to present their theories; their works are submitted to academic journals. Anything pretending to be a scientific breakthru is putrid leftovers that have been regurgitated out of the peer-review system.
Suits in the Inner Flaps - Authors often have pictures and biographies of themselves in the inner-flap. There is nothing wrong with this, but there can be bad signs. Now academics always have public relations problems, and in their books, to solve for this, they typically have pictures of themselves relaxt in business casual or sipping lemonade and smiling. On the other hand, people who have no idea what they're talking about in their books typically dress themselves up and stare at the reader sternly and authoritatively. They're just being pretentious and should be ignored.
Dinesh D'Souza - Anything written or endorsed by Dinesh D'Souza must be stultifying regardless of the topic.
Colored Language Books - Here's a really weird one. Next time you go to the library, go to the section which sells language instruction manuals and step back and look at the shelves. Nearly all of the French books will be blue, nearly all of the Italian books will be green and nearly all of the Spanish books will be a dusty orange. Try it if you don't believe me. Regardless, the colored books are always those most dumbed down as well and should be avoided. Just be sure to avoid the yellow section with even greater fervor: that's Rosetta Stone.