Bokeh

To achieve bokeh in an image, you need to use a fast lens—the faster the better. You’ll want to use a lens with at least an f/2.8 aperture, with faster apertures of f/2, f/1.8 or f/1.4 being ideal. Many photographers like to use fast prime lenses when shooting photographs that they want visible bokeh in.
You’ll want to shoot with the lens wide open, so you’ll want to use a shooting mode of Aperture Priority or Manual. Manual gives you the ability to choose both your aperture and shutter speed, whereas Aperture Priority allows you to choose the f/stop while the camera chooses the appropriate shutter speed for the exposure. You could also use the Flexible Program mode, choosing the widest possible aperture/shutter speed