When it is all said and done, killing my mother came easily.
The Almost Moon by Alice Sebold
Your first sentence should raise questions, without using a question mark. Take the line below: What was feared? And why is it worse? I want to know.
It was worse than I feared.
Gang Petition by Peter St. John
Conflict can be introduced straight away or at least hinted at. Usually something has gone wrong or is about to.
Hale knew, before he had been in Brighton three hours, that they meant to murder him.
Brighton Rock by Graham Greene.
Introducing two characters works well when the relationship between them creates mystery and captures the imagination.
The man in black fled across the desert, and the gunslinger followed.
The Dark Tower: The Gunslinger by Stephen King
Showing characters in unusual settings or situations can be another attention keeper.
They had flown from England to Minneapolis to look at a toilet.
Juliet, Naked by Nick Hornby
By starting at an important, pivotal moment in the story, the reader is more likely to want to continue so that he or she can discover what will happen next.
It was dark where she was crouched but the little girl did as she’d been told.
The Forgotten Garden by Kate Morton
There is no formula for the first line but it should set the tone of the book and reflect its genre. Every author has a unique voice and this is the first chance they have to establish it.
Slowly and painfully, I breathe in, appreciating the life it restores in me.
Hues of Blackness by Rosey Thomas Palmer
My last point is that you shouldn’t get bogged down with perfecting the opening. The best first lines are often written after a novel is completed.