The composer's toolbox: understanding bokeh
Bokeh is the blur, or the compositional shape of the blur, created by points of light that fall outside the depth of field of an image. It often first appears as a happy accident -- but once you discover it, you'll forever covet it. With an awareness of light's direction, bokeh becomes a delightful thing you can anticipate and create with intention.
A wide aperture plus dappled light in your background -- leaves, sunflare, bright objects lit by direct sunlight -- makes for a great backdrop. When you're composing your shot, watch for how the light falls. Open up your aperture, focus on a subject relatively close to you, and watch as the shallow depth of field abstracts the background into sparkling circles of light.