Start shooting with your camera and, before you know it, you'll end up with pictures that have beautifully customized bokeh shapes. Remember, the cardboard contraption that we made here serves as a primary aperture, masking out the shape of the aperture blades of the lens.
Additional Tips
It is important that you shoot with a wide open aperture because the light entering the lens is greatly reduced by the cardboard setup.
Photo by Philgarlic

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Compose your shot with lots of light source in the background to create beautiful patterns.
Photo by dotbenjamin

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As you can see from the images above, adding some foreground objects to your image can definitely add more style to your image, so don't forget to include a foreground subject.
Check out this excellent article and go through the comments section to learn a lot about the above mentioned technique.