What usually catches my eye first (and what I look for) is the title, then the author, then the cover art. If all of that looks interesting, I'll read the covers, front and back, then open the book at random and read a section or page or two. Since I buy most of my 'fun' reading at the local used bookstore, this seems to work well for me. If it's a book by an author I'm familiar with, I'm more likely to pick it up regardless of title, art, or blurbs.

I buy most of my non-fiction online - usually from Amazon as Barnes & Noble made me mad over Christmas - because I usually am looking for something in particular like a textbook for a class or other book recommended for whatever project I might be working on at the time.