What you need:
Your camera A tripod (or means of supporting the camera) so you can deal with low light levels Some card Shapes - craft punches are great for this!
Fairy lights or your Christmas tree lights
1. Draw a circle on your card that is the diameter of your lens - this helps you to centre the shape which is vital for the success of this project. Any shape will do but they need to be reasonable large to work.
2. You can either draw your shape or use a template to cut it out from. I used a craft punch as I wanted to try a snowflake (and wasn't sure about my cutting skills!). Either cut your shape in the centre of the circle or, if using a stamp like me, cut a hole in the centre and then stick the cutout over it.
3. Set up your camera using the lowest aperture possible for your camera or lens. I used F1.8 for these examples using my 50mm lens as it has the lowest aperture of my lenses.
4. I also shot in Manual mode as this allowed me to change the exposure easily. But you could shoot in Aperture priority too.
5. Set your camera/lens to manual focus and adjust until the lights become out of focus. You may choose to shoot using your screen/live view to make this easier.
Hold the card over the lens, making sure the cutout is in the centre of the lens and take the photo.
You should get shaped bokeh!
You can use something in the foreground with the bokeh in the background. To do this make sure your subject is a good distance from the lights otherwise you won't see the effect.
Focus on your subject but remember that if using a very shallow depth of field you will get some softness on your subject.
I found it easiest to focus using Autofocus, turn the lens to Manual and then place the card in front. It solved some focusing issues with the card in place.
I edited the photos slightly afterwards to bring the exposure of the cottages up slightly without affecting the bokeh as I liked the 'night sky' effect of the image.
You will need to play around with this until you get the right results - distance between you and the foreground subject, you and the lights, the size of your shape and placing it centrally on the lens. But once you get it right you'll be able to have loads of fun with it this Christmas!