Slipping a card into its envelope seems like a no-brainer -- unless you're sending the card to an etiquette fanatic. Saved from an unintentional faux pas by both Miss Manners and Heloise, you know that as long as the front of the card faces the back of the envelope, you've done it right.
Fold Up or Fold Down?
Neither method of inserting the card is wrong. By placing it fold up, the recipient can read the message on the card's front as he or she removes it from the envelope. On the other hand, inserting the card with the fold down prevents any extras such as a business card, money, gift cards or confetti from falling out when the recipient pulls the card out of the envelope.