Picking your own format for your own special kind of card, the materials you are going to use and especially the message you are going to include is very important. Collect greetings and card stock materials and decide the layout and themes you want to use.
You can also cut out a picture from your Royalty free Christmas clipart graphic images package and glue them to the paper chain, one picture a day.
The type of clipart that I use is important for all of the different effects that I'm creating. It needs to be a vector drawing for sure, as non-vector drawings are bitmaps that don't resize nicely... they'll just get all bumpy and not look good. Also, I'm drawn to simply line art because if it's too complex sometimes it doesn't look as good in the different sizes. It's also good if it's a single color, usually black, because then I can change it to whatever I want quite easily just using simple graphics software. Just remember, simple is better, is cleaner, and usually creates a more sophisicated look.