Hmmm, maybe I'll tackle this question in a more personal sense than try to answer for other people.
For myself, when I'm looking for something new, I am famous for scanning book covers. I do it ALL the time. I have spent hours roaming a book store, analyzing covers. It's actually how I came upon Brazilian author, Jorge Amado, one of my favorite writers.
Back cover blurbs are important and once the cover catches my attention, I head to the blurb. But this is all very functional and analytic - there are also moments when I know I want to find a fantasy book with a badass heroine, kicking ass and taking names or some hot, love story and I go off in search of them.
Once I dive into the book, I want well-developed characters and the story to move along - I am not a fan of pages upon pages of descriptive prose. But that's just me. I like to read strong women - simpering, weak women bother me tremendously and I tend to avoid their stories.