Framing a Differential Focus Shot
Differential focus is a photography technique that involves using a lens' depth of field to create focus layers within an image. The extreme contrast between objects at different distances serves two functions. It can create a subject to pop out of the rest of the frame which directs a viewers attention to it, and it also creates depth in the frame which makes a two dimensional image appear more three dimensional. When framing a shot that employs differential focus, you need to take focus layering into account.
The Rule of Thirds
The 'Rule of Thirds' is the number one framing guideline that photographers should obey when staging their shot. It basically states that an image looks more visually interesting when the framing is off center. You divide the frame into nine squares and try to position your subject and objects at the imaginary lines that intersect with each other.
Foreground, Midground, Background
With differential focus, you not only have to keep the 'Rule of Thirds' in mind, but you also need to stage your shot to incorporate focal distances too. Instead of just worrying about the 'X' and 'Y' axis, you now also have to worry about 'Z' depth.
Stage your shot with the subject and objects in the foreground, midground and background. Then, choose what will be in focus. If it's an object in the foreground, then that will be sharp, while the midground will be slightly soft and the background will be a blur. If it's the midground, then that will be sharp while the foreground and background will be soft.
How you choose the focal distance is up to you. You're the artist. Just be sure to stage the frame so that it not only looks great, but also incorporates the depth of field to it's advantage to make it appear more three dimensional.