One of the notes of etiquette that have lapsed over the years in common culture is the thank you note. This small sign of gratitude and thanks is rarely more than a single paragraph of text that's sent to a relative that gave you a particularly nice or unexpected gift, or even a friend who let you stay at their place for a holiday. However, the thank you note is also important in business, particularly for people who attend meetings where you want them to know their presence was noticed and greatly appreciated.
Find all the necessary information about the recipient. This includes their receiving address, spelling of their name, and the event you are sending thanks. Assemble the details before you start.
Write a rough draft. This can be done on regular paper, and the note should be brief, genuine, and it should mention specifically what it is that you're thanking the recipient for. In this case for attending a business meeting. If the recipient made any points, shared their experience, or contributed in any other way, this would be the time to mention that and say thank you for it.
Edit your rough draft. Make sure the spelling and grammar is correct, that the note is of the proper length, and that you mentioned everything you wish to. Make all changes now.
Re-write your thank you note on good stationary. These notes should be written by hand to give it a personal feeling, and when possible you should make sure that the note looks professional and presentable. While it isn't recommended that you type the note, for some people with exceptionally poor handwriting this may be a better option.
Be genuine, polite, and end your thank you notes on a positive upswing.