I know it's early for Christmas cards, but you could use the same technique to make Halloween, Mother's Day, Thank you cards etc... I like these cards because all you have to do is create one block design, which can be used over and over again with different colors.
This is the kit I bought at a local arts and crafts store
Create your design on a piece of tracing paper
Transfer your image onto the wood block. If you are creating numbers or letters, make sure to transfer them reversed. That way, they will be the right way round when you print them
Carefully carve your design. I made an intricate design so it took a while.
Once your design is all carved out, you can start printing!
Lay your block down so that the design is facing upwards.
Lightly dab acrylic paints onto your block
Use enough paint to cover the block, but make sure not to get paint in the crevices
Place a piece of card stock over the wet paint and use a roller to transfer the paint.
Let the paint dry. You can even use you block print on fabrics and walls.