The answer is, I shoot with a low aperture - also known as a shallow Depth of Field.
This is one of the first things you learn in photography, it’s part of the Exposure Triangle.
In it’s simplest form, the lower the aperture [f stop] the more blur [Bokeh]you will achieve. The image below is a comparison using pictures straight out of the camera and shows how the aperture effects the amount of Bokeh in an image.
Shot with a Canon 85mm
The Canon 85mm f1.8, has 23 f stops from 1.8 up to 22.
I tend to shoot at between f2 and f4, resulting in Bokeh like this.