For the next few days I will be airing my favourite first lines - and looking at why I think they work.
Chesil Beach by Ian McEwan sets the topic of the novel with his introductory sentence: They were young, educated, and both virgins on this, their wedding night, and they lived in a time when a conversation about sexual difficulties was plainly impossible.
This novel is immersed in sex and intimacy, and this first sentence immediately introduces the reader to the characters and their challenge.
The Story of a Marriage by Andrew Sean Greer begins: We think we know the ones we love
This beginning tells the reader that someone faces being unmasked and I, for one, wanted to know more.

A Visit From the Good Squad by Jennifer Egan starts: It began in the usual way, in the bathroom of the Lassimo Hotel.
Ohhh! Hotels, so many possibilities for an unknown character - and in the bathroom! Well, I wanted to know more.
These first lines are all very simple, and draw readers into the story in a very old fashioned way: It was a dark and windy night.... This plain hook opens up so many possibilities. 
To me, the best first line is a simple one.
But you can disagree.