Politely state your purpose in the first line. If you have started it "Dear Sir", you mustn't end it "Yours sincerely" but "Yours faithfully". When writing the address on the envelope, keep each line flush along the left margin, not edging steadily rightwards as though the letters are descending a staircase like Joan Collins in Dynasty. These are the letter-writing precepts I was taught at Palmers Green girls' junior school in north London, along with lessons in blotting paper and fountain pen use.

I still have that first Parker pen, its soft nib blunt and wide with age. These days I write in turquoise ink with a Sheaffer pen so smooth, silent, heavy and perfect it's like driving a limo at midnight. In my desk drawer is a collection of cards from the V&A, and on the windowsill a rainbow collection of Smythson Panama notebooks.

Like many writers I love letters, notes, diary pages and memoranda. We might be a dying breed. A poll to mark National Letter Writing Day has found that 10% of seven- to 14-year-olds have never handwritten a letter, though half had sent an email in the previous week.

I am not inclined to feel worried that seven-year-olds are no longer being made to write stilted, ungrateful thank-you letters to grandparents they could just as easily text, phone or email. Though I wince at textspeak, modern-day acronyms and slang, young people's emails and blogs are witty and fast-talking, and they are probably communicating more than ever. Chattering, joking, showing off, jibing, wishing and grandstanding are what young people do. As long as they can actually write by hand, and practise in class, the desire to write postable letters to others will come naturally, probably later in life.

The structuring of a good thank-you letter, necessary for the perpetuation of pleasant social etiquette, can be taught easily. But a real letter arises naturally from a deep surge of serious emotion: love, sympathy, sadness, chagrin, desire, joyful friendship. And though they may be spelled out in plain old Quink, they're really written with our hearts' juices. Letters form turning points in several of Jane Austen's novels: there is Darcy's revelation of Wickham's true nature in Pride and Prejudice, and Wentworth's declaration in Persuasion.

It's hard to lie when writing by hand. Nobody, I hope, wastes their (or their recipients') time setting out words they don't mean. Letters require effort and the kind of diligence only sincerity can fuel. You'd have to be a proficient and vicious con artist to fib your way through an entire handwritten letter. We keep the letters sent to us because they mean something. They carry the touch of the writer and retain the warmth of their sentiments, which is why the burning of letters can feel so profane, and their loss so jarring.

One must take care to direct one's letters to a worthy recipient. The only thing sadder than sending wordy best wishes to someone with a jeering mind and faithless heart is writing to a doomed fictional character. A new film, Letters To Juliet, tells the true story of The Juliet Club, volunteers from Verona who answer letters sent by lovelorn advice-seekers to the heroine of Romeo and Juliet. They receive more than 5,000 annually, 90% handwritten.

I would not write to Juliet for advice, as her romance ended with her own death and her lover's. Their love strategy turned into a tragedy not because their families could never get along, but because of a farcical plot mistake that has the audience cringing at the importance of timing. The hopeful correspondents of Juliet's Club may be misguided, but their words are sincere and their wishes timeless.

Will the desire to write letters ever dry up? Answers on a postcard please.