Check out this little trick to put them up.
1. Start with a roll of twine and mini clothes pins.
2. Measure out a healthy amount of twine to tie around a closet door from top to bottom.
3. Grab your stack of Christmas cards and attach the card to the twine with a small clothes pin
4. Start from the top and work your way to the bottom and BOOM, you got your cards on display for the season. Happy Holidays!