One way to write a thank you note showing your gratitude is to hand-write the note. This expresses your gratitude by showing you are willing to take the time to elegantly compose thoughts instead of quickly typing them. It is acceptable to use informal stationary and printed labels.
Begin the letter itself with "dear" followed by an appropriate name. For friends, use their first names, but for people you do not know that well, use their last names.
The first sentence of the letter should explicitly thank the individual for what they have done for you, and be specific about dates, gifts, and other pertinent details. Use the second sentence to express how you will use what he has done for you. An example of this is a student thanking someone for a monetary gift and explaining that he just bought the textbooks he needed thanks to his benefactor's generosity.
Use the final sentence to address the connection you have with this person and emphasize your enthusiasm for time spent with this person. An example is the same student telling his benefactor that he will be home over the Winter break and that he is looking forward to seeing that person again.
End the letter in a friendly manner, such as saying "thanks again," and then sign your name.