It is a truth universally acknowledged -

- that the opening lines of a novel must grab the reader's attention immediately.

Having chosen a name for my central character, and decided exactly when the story is to take place,  I'm now thinking about the first chapter.

Most editors and agents agree that the novel should begin when the action begins. So no long scenes of introspection as the heroine looks back over her life to this point (that's what flashbacks are for, after all). She needs to start her new job/meet the hero/find the body within the first few pages.

It's unlikely that the extended infodump with which Jane Austen began her first published novel, Sense and Sensibility, would get it beyond the slush pile today. Nor the long and convoluted sentence with which Dickens began his first published novel:

The first ray of light which illumines the gloom, and converts into a dazzling brilliancy that obscurity in which the earlier history of the public career of the immortal Pickwick would appear to be involved, is derived from the perusal of the following entry in the Transactions of the Pickwick Club, which the editor of these papers feels the highest pleasure in laying before his readers, as a proof of the careful attention, indefatigable assiduity, and nice discrimination, with which his search among the multifarious documents confided to him has been conducted.

Other authors managed to be more concise in their opening lines: 

In the year 1878 I took my degree of Doctor of Medicine of the University of London, and proceeded to Netley to go through the course prescribed for surgeons in the army.

I returned from the City about three o’clock on that May afternoon pretty well disgusted with life.

'Oh damn!' said Lord Peter Wimsey at Piccadilly Circus.

Scarlett O’Hara was not beautiful but men seldom realized it when caught by her charm as the Tarleton twins were.

In a hole in the ground there lived a hobbit.

Mr and Mrs Dursley of number four, Privet Drive, were proud to say that they were perfectly normal, thank you very much.

It started at one thirty on a cold Tuesday morning in January when Martin Turner, street performer and, in his own words, apprentice gigolo, tripped over a body in front of the East Portico of St Paul’s at Covent Garden.

Dorothy L. Sayers managed to compress the most information about character and setting into the smallest number of words. She was an advertising copywriter who knew how to get a message across succinctly.

It's desirable to include dialogue as early as possible, but that means someone has to be provided for the character to talk to.  Lord Peter is speaking to a taxi driver, who is there solely for that purpose and plays no further part in the story. 

I already know that my character will have a friend and what the friend's personality will be.  I think that instead of introducing her later, as I originally planned, she and my central character will bump into each other, and have a conversation, in the first few pages.

Now I need to decide on the friend's name  - and on the opening sentence.