Cafe society: At least once a week I go into Nicolsons, the cafe in Edinburgh where I wrote much of my first novel, Harry Potter and the Philospher's Stone. The manager and owners are friends these days - or maybe they're just relieved I now order food. I do most of my press interviews in the cafe partly out of gratitude for all the times they let me sit over one cold espresso for two hours.

I don't often write in there these days because I feel too self-conscious, but I did a radio interview two days ago and it's quite difficult to answer questions sensibly when half the staff, your sister and your daughter are giggling insanely across the restaurant about how stupid you look in a pair of headphones.

Overnight sensation: This time last year an American publisher bought the rights to Harry Potter and the Philospher's Stone for what they call a "substantial sum". My life changed literally overnight. I put down the telephone to my agent, Christopher, in a state of advanced shock (I think my contribution to the conversation consisted almost entirely of the words "How much? I don't believe it"), walked around my flat for hours in a kind of nervous frenzy, went to bed at about 2am, and was awoken by the telephone early next morning. It didn't stop ringing for a week. It was a Cinderella story for the press; broke, divorced mother writes in cafes while her daughter naps beside her, and finally strikes it lucky. I had never expected anyone to be interested in me personally; my wildest fantasies hadn't gone much further than the book being published and the pinnacle of achievement seemed to me to be a review in a quality newspaper. Suddenly to see my own grinning face looming out of half a dozen papers, all captioned along the lines of "penniless single mother Joanne Rowling", was a disorientating experience.

Roll up, roll up: I've just come back from a series of public signings and readings in bookshops and schools in England and Scotland to launch the second Harry Potter book, Harry Potter and the Chamber of Secrets, and it's been one of the best weeks of my life. I've met 10-year-olds who have turned up with their own stories to show me, girls who have passed me fan letters, purple with embarrassment, boys who have stared at the floor while their mothers poke them in the small of the back, urging them to tell me how much they liked the book ("He couldn't put it down, could you, Daniel? You've read it six times, haven't you Daniel? Haven't you Daniel? Say something, Daniel.") The very best moment was meeting the mother of a dyslexic nine-year-old, who told me Harry Potter was the first book he'd ever finished all by himself. She said she'd burst into tears when she found him reading it in bed the morning after she'd read the first two chapters aloud to him. I'm not sure I managed to convey to her what a wonderful thing that was to hear, because I thought I was going to cry too.

As a former teacher there is a blissful feeling of irresponsibility in facing a roomful of children and knowing all you're supposed to do is to entertain them and to hell with keeping discipline. I must say, though, that not one of the children I've seen in the last week has been anywhere near as rude as the pair of teachers who sat talking right through my reading while 60 beautifully behaved children sat listening to every word.

I wanted to stop and say loudly, "We'll wait until you've finished your conversation, shall we?" but I am a coward so I merely read more loudly.

Sour gripes: Public signings occasionally attract members of a scary breed: the Unpublished and Indignant Writer. I used to belong to a more pathetic sub-species (Unpublished and Depressed), so the mentality of Mr Indignant is difficult for me to fathom. I always assumed that the publishers who turned down Harry Potter and the Philosopher's Stone did so because, in their opinion, it wasn't good enough. Mr Indignant, however, is not so naive. He knows that there is a trick to getting published, a knack that has little or nothing to do with having written a book people might enjoy reading. Therefore, when he sees that a recently published writer will be appearing at his local bookshop, he pops along to demand the magic formula.

I met a particularly persistent Mr Indignant this week. He approached me with a fixed and slightly maniac grin, and opened the conversation by informing me that Bloomsbury (my publishers) had turned down his book. There followed an inquisition on how I had managed to worm my way onto their list which stopped just short of suggesting I possessed incriminating photographs of the managing director.

I know how miserable it is to hear the thud of your rejected manuscript on the doormat because it was happening to me not very long ago, but the only advice I feel qualified to give unpublished writers is: look up suitable agents and publishers in the Writers' and Artists' Yearbook and work your way through the list.

It is boring advice, perhaps, but it worked for me. In the end Mr Indignant gave me up as a bad job and cornered Rosamund, who is in charge of marketing Bloomsbury's children's books. The last I heard, he was telling her he'd already devised his own marketing strategy.

Listen with mother: I came home after the book tour, baggy-eyed with exhaustion and laden with presents, to an only mildly enthusiastic welcome from my four-year-old daughter. She had been staying with her best friend, Thomas, who has a bunk bed and an extensive collection of Batman toys - I can't compete. In an attempt to whip up some excitement after the last Nicolsons' interview, I turned on the radio that evening and told her she was about to hear mummy talking about her book. She looked at me in a pitying sort of way. "But I already know what you sound like, mummy."

Harry Potter and the Chamber of Secrets is published by Bloomsbury, priced Pounds 10.99. It is already a bestseller