This is how I read.

I don't ever read the backs of books. At best, it gives me no idea of the author's writing, and at worst it can ruin the plot. What a book is about isn't as important as my emotional response to reading it. You have to trust the author enough to just start reading.

I know, books aren't cheap, and you've got to have some way of narrowing the field. You have little choice but to judge a book by its cover, and more importantly its title, and, let's be honest, probably the author's photo. Once it's passed these tests, open it and read the first sentence, the first paragraph, the first page. Sometime you'll know by the first sentence. If you're interested enough to turn the page, standing in a bookstore, you should probably buy it. 

Which brings us to another point, which is: Ask a bookseller (or a friend, but booksellers need the work). There's hopefully an independent bookstore near your home, with a quirky staff just waiting to flex their intellects in your direction. A friend says she's intimidated to ask booksellers for recommendations, and I can see that; there are those whose puffed up brains get the better of them, but most of us are friendly if slightly socially awkward. And don't buy books online (if you don't have to). Books aren't that expensive, and you're not really that lazy. 

Also important: If you aren't enjoying a book, stop reading it. As long as you haven't spilled coffee on it or ripped off the cover, you can take it back. There are too many great books in the world to keep reading one that doesn't do it for you.

Some examples of books I've chosen based on the cover and/or title:

Jonathan Strange and Mr. Norell (the galley was two toned black and white with magic symbols)

Sacred Games (also the galley-it had a gold spine and a slipcover with bullet holes. I'm a sucker for a slipcover)

The Raw Shark Texts (every bit as kick ass as the title)

The Girl on the Fridge (very weird, very short stories)

The Glass Books of the Dream Eaters (nowhere near as cheesy as it sounds)

Alternatively:

 I refuse to read any book with wife or daughter in the title. And there are so many of them to  reject:

American Wife, The Senator's Wife, The Zookeeper's Wife

The Memory Keeper's Daughter, The Heretic's Daughter, The Abortionist's Daughter

 I cut a sideways deal with The Time Traveler's Wife, which I listened to on CD after many many. It was great, but I still think this is lazy titling.

A short selection of really great beginnings:

"Grandpa Slavko measured my head with Granny's washing line, I got a magic hat, a pointy magic hat made of cardboard, and Grandpa Slavko said: I'm really still too young for this sort of thing, and you're already too old." How the Soldier Repairs the Gramophone, by Sasa Stanisic 

"The beet is the most intense of vegetables. The radish, admittedly, is more feverish, but the fire of the radish is a cold fire, the fire of discontent not of passion. Tomatoes are lusty enough, yet there runs through tomatoes an undercurrent of frivolity. Beets are deadly serious." Jitterbug Perfume, by Tom Robbins

"Early in the morning, late in the century, Cricklewood Broadway. At 0627 hours on January 1, 1975, Alfred Archibald Jones was dressed in corduroy and sat in a fume-filled Cavalier Muskateer Estate facedown on the steering wheel, hoping the judgment would not be too heavy on him." White Teeth, by Zadie Smith

"In accordance with the law the death sentence was announced to Cincinnatus C. in a whisper."Invitation to a Beheading, by Vladimir Nabakov

"On July 26, 1971, while legendary photographer Diane Arbus was curled in a bathtub at the Westbeth apartments in New York City, slitting her wrists, Bob Langmuir was travelling out of his body, which was heaped in a roadside ditch in rural Vermont, struggling to maintain its own hold on life." Hubert's Freaks, by Gregory Gibson

This last one I just found today. I can't wait to read it.