If you have not been saving Christmas cards, now is as good a time as any to start. You can also look for inexpensive boxed sets at dollar stores. I picked some up recently at two boxes for $1.00 (these are likely last year’s designs put on sale to make room for new ones, but they work).
For a mantel or a shelf, you can arrange bare branches or (real or artificial) pine boughs along the length. Drape with tiny white lights. Then, tuck in Christmas cards as you receive them or use some you already have. It makes a nice display and you can add little clusters of berries, pinecones, or tiny ornaments if desired.
Make ornaments from old Christmas cards. Cut them down to small squares, glue them closed, and punch a hole in the top center when dry. Thread ribbon through the hole and hang them up.
You can also make great gift tags from old Christmas cards. Remove the front cover and cut it into strips just the right size for tags. Make sure each strip has a bit of imagery and try to cut them out accordingly. Punch a hole and add string or ribbon. Write names on the back. An alternative method is to cut them out so none of the strips actually have an image but instead all appear abstract. Then, cut away the blank areas from the back of the card and use those pieces to mat the colored portion. Write “to” at the top on the blank part and “from” on the bottom.
Another cool trick to use with Christmas cards is using them to dress up a vase. Place a colored vase inside a larger clear one, and place Christmas card covers in the space between the two (or just place one in the front).