Get a heavy card paper of a A4 sheet paper length fold the card paper from the middle making it shape like a card, write with penciled letters in a small font on the border line of the card write on the border line inside and outside you can write anything that she might like i.e. I love you marry Christmas, I miss you wish to meet you this Christmas just write anything should read with a smile on her face.
Get some Christmas themes that you would like to paste on the card i.e. Santa clause with a heart in his hand, a Christmas tree with a Heart on top or any theme that would give out an image of love and affection on Christmas.
Start writing a beautiful message for your girlfriend telling her how special she is and the difference she make while being near you this Christmas, humor is good as well something that she would like to laugh at as well.
If you have a picture of you guys together scanning that and printing it would be a really good idea you can glue the picture inside the card on any empty space.
Finally finish off the card by soothing the edges with a pair of scissors and gluing stickers and cute clip art on the cover page.