I know a woman who can get people to do whatever she wants. She can make busy executives give her their evenings, their thoughts and their money. On various occasions, she has persuaded me to do things for her, just as she has enlisted thousands of others.

I ran into her the other day and asked what her secret was. "It is not hard," she said. "I just say 'please' and 'thank you'."

Actually it is not quite as simple as that. Most people know how to say "please" and "thank you" - or think they do. Almost everyone was taught before they went to primary school. But hardly anyone has been taught how to do it properly.

Consider the following perfectly polite e-mail I received recently from a man I know slightly. It began: "This year we are partnering with XXX to launch the second annual YYY conference. I know you are busy but we would love you to host a session on women in business on the Saturday."

It went on at length about the theme of the year and offered a link to a video of the previous year's event. "Do let me know if that is feasible," it ended. Why would I give up a Saturday on the basis of watching a clip of a similar conference a year earlier?

The length of the e-mail made me feel restive and inclined to hit the delete button. To be reminded that I am busy merely provided an excuse to decline.

Now consider this message from my other acquaintance. Its subject line read, "If only you would..." and the e-mail continued "... join our panel on xxx. We have a lot of clever but worthy people talking, and we need your genius to liven it up. Please say yes."

What this does is cut to the chase - and the chase is flattery. The only truly effective way of saying "please" is to butter people up.

There is no danger of ever laying it on too thick. There is no level at which flattery stops working, according to a study by Professor Jennifer Chatman of the University of California, Berkeley.

In addition to being flattering, the perfect "please" has to make you feel not only wanted, but also needed. I read the e-mail and said "yes" at once. I knew how manipulative it was, but I could not help myself.

Getting "thank you" right is just as easy, though just as uncommon.

Consider the failed attempt that landed in my inbox recently: "Thank you for talking at our function last week and for giving up your time. The feedback was excellent and we hope you enjoyed it."

This was polite and professional. Yet it quite failed to do its job. For a start, it was too slow. An e-mailed thank you should arrive within hours, not the following week.

Equally, to be thanked for your time is singularly ungratifying. Time takes no skill to give. To say the feedback was excellent was too vague to be convincing. And rather than ask if I had enjoyed it, it would have been better to attest how much they had enjoyed having me.

In rejecting this message, I felt the spirit of my mother. She was a fiend with the thank-you letter.

Every year on Dec 27, she sat us children down and made us write letters to everyone who had given us anything for Christmas.

We had to specify what the present was, claim to be delighted with it and - this was hardest - we had to say why. When we were done with thanking, we had to keep writing until half way down the second page before signing off.

Three of my mother's four principles apply to the thank-you e-mail. You thank specifically for the thing. You say why you liked it - and you must thank promptly. The only difference for me now is that I no longer have to rattle on for a page and a half.

Indeed, the shorter the better.

And this is exactly what my persuasive acquaintance did.

"Extraoooordinary", said the subject line of the thank-you e-mail that was waiting in my inbox when I awoke the next day. "Thank you for bringing the evening to life and for scorching wit and sense. You are our own Tina Fey."

Actually, I had performed indifferently. I knew that - and so did she. We both understood the game she was playing. But no matter. The next time she asks me to do something, I will comply.

FINANCIAL TIMES