Melissa Bank has been hailed as an expert on modern relationships. Six years ago, she wrote bestseller The Girls’ Guide to Hunting and Fishing, soon to be filmed starring Sarah Michelle Gellar. Now she has a new novel. But, she confesses, she still doesn’t feel grown-up

Sophie Applebaum, the heroine of Melissa Bank’s new book of linked short stories, works for a time in advertising. But, as she tries to explain to her mother, not all advertising jobs are alike.

’What kind of advertising are you in?’ her mother asks. ’I write junk mail, Mom,’ comes the reply.

Melissa Bank’s bestselling first book, The Girls’ Guide to Hunting and Fishing, was written over 12 years of evenings in her office at McCann Erickson, where she spent her days dreaming up slogans for sanitary towels.

’After all those years,’ she says when I meet her for coffee near her home in New York, ’I know that someone writes everything - everything - in a way that other people don’t. I remember working late at the office; I was in the bathroom at about one in the morning, after the cleaning crew had just come. All the rolls of toilet paper were wrapped up, and I noticed on the wrapping itself - "Ideal for use with septic tanks". I thought, somebody wrote that, and all she wanted to say was, "This is perfect for toilets", but she came up with 10 lines and the client chose this one. That’s what I was doing all the time - "Ideal for use in septic tanks."’

In a way, this is as good an introduction to Bank’s heroines, and to the humour that drives her writing, as any: the brilliantly hopeless occupation (’Working really hard at writing something that people throw out,’ as Bank puts it), the doggedness of the late night at the office, the invisibility and the knowledge it gives her - a sensitivity to written messages of all kinds, whether it’s the fiction of Nabokov or the label on a packet of loo roll.

Bank has just come back from a holiday in Mexico, where she and her boyfriend stayed in a hut on the beach. She has the tan and the bleached hair of someone who has spent her life there, and long, muscular legs that stretch out from under a white denim miniskirt.

But her direct gaze and slightly crooked smile are pure New York and she speaks in a languorous voice that seems to say, in its very tone: no irony in life passes me by.

Though she has been hailed as an expert on modern relationships, Bank is mostly too busy writing to go out. She doesn’t like her work to be classified as ’chick lit’. And as for Sex and the City - she doesn’t even own a television.

Bank admits to having ’an inordinate amount of angst’ when it comes to writing. She says she could have spent another five years working on her first book, and since the proceeds from that one allowed her to give up her job, she worked on The Wonder Spot ’24 hours a day’ for six years. She feels like she ’killed brain cells’, she worked so hard.

Though The Wonder Spot bears certain resemblances to The Girls’ Guide - the sharp-tongued narrators both have a wry relationship to life; the short-story structure is the same - the sentences in this one are cleaner, quicker, more mature. It shows no sign of the hefty labour Bank describes and trips off the page with wit and ease. ’You know what?’ she says when I tell her this, ’I could have made it easier. I know that certain writers suffer from being called accessible. And I do worry sometimes that people won’t think of this fiction as "serious". There are certain kinds of literature in which you don’t necessarily know what’s going on or who’s speaking. But I feel like I spent my life just wanting to know what’s going on, so in my fiction I don’t want people to feel like they don’t know what’s going on.’

The Wonder Spot follows Sophie Applebaum from adolescence to college and beyond. It opens with a hilariously sulky story about having to go to Hebrew school in the suburbs of Philadelphia. (Her too-perfect cousin Rebecca is, in the words of the 12-year-old Sophie, ’like a long piece of hair with hair’.)

At university, Sophie’s world is coloured by her room-mate, Venice, who glides in from Antibes full of glamour and useful information (such as: 90 per cent of men have lesbian fantasies and the other 10 per cent are gay).

In New York, the seemingly Herculean task of teaching herself to type stands eloquently for the postponement of reality while Sophie looks for her first job. We meet her brothers, now grown up, and her lovers or would-be lovers: Josh, Neil, Matthew, Bobby, Seth.

Her younger brother wants to introduce her to a paediatric heart surgeon. ’That’s good,’ she says, ’I have a paediatric heart.’

Her older brother is in love with a woman who wants him to hit her in bed, but he can’t bring himself to do it. ’Can I hit her?’ is Sophie’s response.

Essentially, it’s a book about moving on and growing up and although Bank is surprised by the extent to which people have looked for correspondences between her fiction and her life, her upbringing was, she confesses, ’similar to the book’.

She grew up in a suburb of Philadelphia, her father - ’kind of an archetypal father’ whom she wanted to please - was a neurologist who died of leukaemia. (In the book the father’s death is passed over; we cut straight to the family’s bereavement.) The kind of thing that doesn’t happen to Sophie, however, is what’s happened to Bank as a result of her work.

From the very beginning of her literary career, when The Girls’ Guide was written in part for Francis Ford Coppola’s Zoetrope magazine, Bank’s writing has been critically esteemed, financially rewarded and optioned for the movies. (She received a letter from Joseph Heller; he’d been mean about The Girls’ Guide before he’d read it and he wanted to apologise and say how much he liked it.)

Having been through several screenplays, including one written by Bank herself, The Girls’ Guide is now due to be brought to the screen by Peter Chelsom, the director of Serendipity, and will star Sarah Michelle Gellar of Buffy the Vampire Slayer fame.

Bank hasn’t adopted any grand lifestyle, though. She still lives in a one-bedroom apartment in Chelsea, in a building where her brother also lives. He met his wife in the building (they now have two kids), and Bank met her own boyfriend there. ’I have great friends in the building,’ she says. ’That’s why even though the apartment is tiny, I don’t think I’m ever going to be able to leave.’

When I ask Bank when she felt she’d grown up, she says her father’s death made her grow up fast, but also that she feels she is always growing up.

’And I also feel that most of my friends are all different ages,’ she explains. ’You know how on the Upper West Side you see women with a really unified personality? With a stroller and a five-year-old; she’s 37. Everything is sort of more in line. But I feel like there are people who are more like me: you’re a seven-year-old, you’re a 14-year-old, you’re 43, you’re 27.’

She adds: ’I think I’ll always feel like I’m growing up. I’m always figuring things out.

· Melissa Bank and Nick Hornby will be in conversation at the Criterion Theatre, London W1 on 13 July; tickets: 0870 990 1299