The Simple Dollar blog has these easy tips for writing a perfect thank you note ...
1. Always start with Dear;
2. Say thank you (either start with "Thank you for" or express comment "It was wonderful seeing you .. , then lead into thank you)
3. Express what you plan to do with it or what it means to you;
4. Build towards a future connection ("I hope we can ...", "I hope to hear ...")
5. Sign it in friendly way ("Thanks again,")
1. Must be in writing
2. Must sound natural (try typing out first, then write on note card)
When to send:
1. Response to a gift
2. When you interview for a job (even if it didn't go well)
3. When someone does something meaningful for you
If you check out the comments section on that blog there are other samples of thank you notes that can work for gifts and following job interviews.