Write a strong first line that makes the reader want to know more.
“From the first line, a story should create a sense of character, conflict, setting, mood, theme or style, or any combination thereof. Most importantly it should make the reader ask questions.” – Diane Callahan, Editor, http://www.quotidianwriter.com
A good example of these factors in one piece is Silvia Plath’s The Bell Jar:
“It was a queer, sultry summer, the summer they electrocuted the Rosenbergs, and I didn’t know what I was doing in New York.”
Or the opening from Donna Tarrt’s The Secret History:
“The snow in the mountains was melting and Bunny had been dead for several weeks before we came to understand the gravity of our situation.”
Do not think you must include all the elements above, or that your opening lines need to be quite so gloomy.
Take PG Wodehouse’s start to The Luck of the Bodkins:
“Into the face of the young man who sat on the terrace of the Hotel Magnifique at Cannes there had crept a look of furtive shame, the shifty, hangdog look which announces that an Englishman is about to talk French.”
Callahan has broken down the essentials into the following overall elements you need in your opener.
Does your opening shot contain or form a question in the mind of the reader?
Is there some hint at the character of either the narrator or main character, or indeed the character of the author?
Is there imagery which will be enticing for the reader and is fitting to the story?
Does the beginning of the story hint or explicitly state what the overall sway of the novel will be?