Find your favorite Yule clip art online, and use it as the front of your card. Use your word processing program to write a greeting for the inside.
You'll need black card stock for this one, as well as a variety of bright colors to create your design. Create a sun or other design by cutting small pieces in bright colored paper. Place them on the black card stock, leaving black lines between the colored pieces, creating a mosaic or stained-glass effect. On the inside, paste a light-colored strip of paper for the written greeting.