We don't think we're going out on a limb when we say that most people are terrible at writing proper thank you notes. Liz Danzico, however, is not. Her article "On 'thank you,' or why Socrates was wrong'" outlines a few simple guidelines to writing an effective thank you.
The formula is quite simple: when someone does something for you: say thank you. Nothing could be simpler, and nothing could be more valuable.
It was an invaluable piece of advice that I've followed in my adult life, writing thank you notes for all things -- big, small, monumental, and frivolous. And always within 48 hours of the happening. All very personal. Never a Hallmark. Never a pre-printed affair. Never the same twice. Always something I have to dash off myself.
But there is some fitness to writing the thank you. Or at least a handful of things to keep in mind. Here are my guidelines to writing the critical note:
Thank you notes are tangible notes whenever possible.
These notes are all done by hand whenever possible, sent via USPS mail. A follow-up-thank-you (a thank-you for a gesture on a second occassion) may be done via email, SMS, DM, Facebook, or whatever your choice of media (discretion should be used, depending on nature of thing); regardless, the text should be composed with care.