Firstly you need to draw up a rectangle on some thin cardboard(preferably from cereal or shoe boxes). About 13x17cm(5.1x6.7 inches) And cut out.

Fold the cardboard in half.

Adhere double-sided tape around the edges but don't stick any directly across the fold. I filled in the gaps with a little bit of glue(gluestick type). Quickly stick cardboard on a piece of newspaper.

Print out a christmas image that will produce a clear silohette, I printed them out in varying sizes so I could mix and match between the cards.

Using a good quality craft knife to cut around the edge of your image.

Stencil the christmas image onto the front of the card. I did mine in the right hand corners or as I chose to on one of the cards, I used a big bauble right in the centre. Then cut through carefully with your craft knife.
[Just make sure you don't snap the tip of your craft knife like I did!]

Lightly paint around the outer edges and on the edges of the cut out image. Any christmas colours will work: gold, green, red, white or a mixture of a several.

Wait for the paint to dry and then write your greeting and inner message onto the card using a calligraphy-style felt pen.

Brush a coat of varnish round the edges(or all over) to seal them. You could also use ModPodge or even clear drying PVA glue.