Sorry to harp on about these, but when browsing a book shop I am more likely to read the first line than the back cover. A good first line will make me read on, perhaps even to the end of the page. A bad first line, one that lies in a quagmire of unprepared detail, can make me shiver as I shut the page fast before it leaks out. Consider:
 The news about Walter Bergland wasn't picked up locally - he and Patty had moved away to Washington two years earlier and meant nothing to St. Paul now - but the urban gentry of Ramsey Hill were not so loyal to their city as not to read the New York Times.

Why should we care about Walter, Patty, St. Paul, Ramsey Hill and readers of the New York Times?  If this had not been written by Jonathan Franzen, I would have gone no further in the novel.  
 Aged nine, Stephen standing outside the fur-storage depot where his father works, his sturdy legs in shorts planted on Californian ground.
I love the work of Linda Grant, but this first line from We Had It So Good could have turned me off a novel I actually enjoyed.

 Howard Jacobson's The Finkler Question was a novel that left me cold, but the first line drew me in:
  He should have seen it coming.
Who? What? Why? Immediately I want to know - although later in the novel, I couldn't have cared.

 Sarah Winman's When God Was A Rabbit sets the scene nicely with:
  I decided to enter this world just as my mother got off the bus after an unproductive shopping trip to Ilford.
This gives a sense of place and truly made me want to read on.

 The first line is a delicate balance between giving too much unnecessary clutter and hinting at a scene that draws the reader forward, curious to know more.

I look forward to your thoughts.