Heres the no-brainer formula behind all successful thank-you notes.
Handwrite it, even if you don't have the best penmanship (on stationery is best).
Don't worry about length. Brevity is the soul of a note! But no one liners.
Identify the reason you're thanking someone. Write "the fruitcake was delish!" even if the only thing that ate it was the garbage disposal.
Say something about how the gift makes you feel or what you'll do with it (i.e., "That Warhol catalog looks fabulous on my coffee table. Now, where are m fifteen minutes?").
Make a reference to seeing that person soon (i.e., "Looking forward to seeing you soon!")
Be aware of how to sign off at the end of the note. If you're friends by not close enough to use the word "love," just draw a happy face or write "xoxo" to stand for hugs and kisses. The phrase "best," "all my best," or "cheers" is a casually cool ending for friendly acquaintance, work "friends," and people you don't know well but would like to. "Respectfully," and "regards" work for anyone you have a formal relationship with.
Include your full return address, especially if you don't know the recipient well.