Finally, you need a relatively large aperture (small f-number). Switch your camera to aperture priority and dial in the biggest aperture you can. Unfortunately, this is where a lot of less expensive lenses and smartphones fail to measure up, because you want to be able to open the lens significantly--to f/3.5, f/2.8, or even f/2 if the lens can go that wide. Generally, the wider the better.
How lenses affect bokeh
The same scene taken by two different lenses can look quite different. Consider, for example, the difference between a five-bladed lens and a nine-bladed lens. You can clearly see the difference in the shape of the lights in the examples below.
The bokeh you get from lenses with fewer blades can have a more geometric look, and that's why some photographers go out of their way to use specific lenses for a certain bokeh. Inexpensive five-bladed lenses, for example, tend to give you lots of blurry pentagrams. And check out this crazy bokeh, which looks like a bunch of tiny donuts:
To get this particular look, you need a special kind of lens called a catadioptric lens--it's essentially a mirror telescope. The hollow center in the bokeh is a result of the small secondary mirror in the lens that reflects light from the main mirror into the camera sensor.
Sign up for CIO Asia eNewsletters.