Important topics to include in a gift thank you letter include sincere thanks, the item's intended use, a mention of the occasion when the gift was received and a signature. Written notes are a gracious way to communicate.
Handwritten thank you notes are more meaningful than an email message, according to an article in The Morning News. A simple "thank you for the sweater, the color is perfect" is a great opening. "I enjoyed spending time with you at my birthday party" acknowledges the occasion. It is also appropriate to follow that with "I hope you are well." It is fine to say thank you again before closing with "sincerely," "yours truly" or "love," followed by a signature.