Good Composition - How to Get a Good Figure to Ground Relationship
There are basically two ways to get good figure to ground. One way is through post processing and the other way is paying careful attention to composition when shooting.
Post Processing
The master of using post processing to get flawless figure to ground separation is Magnum photographer, Steve McCurry. If he needs to separate objects, he is willing to take one or more of the objects out using Photoshop. Another post processing technique is to use the dodge and burn tool. A background can be made more dark and the subject more light, or vice verse, to help create separation.
In-Camera
The second way to get figure to ground separation is being attentive to getting it in-camera. That seems to me to be a more authentic choice for street photography. Here are some things that you can do.
Go fishing.
As street photographers, we often find the subject first and allow the background to be a matter of chance. Getting good separation of your subject from the background may or may not happen. To improve the odds, you can fish. One way to fish is to find the background, then the light and finally wait for the right subject.
Another way to fish is to find the scene you want to shoot and then move around until you get the best separation.
Look for light.
Bright light on the subject with receding light in the background will help separate the subject. It will also increase the impression of depth.
Shafts of light can illuminate the subject.
Shoot against the sun. Backlighting can make your subject a silhouette, which generally results in very good separation.
Look for tonal contrast.
Use a flash.
Use selective focus by choosing a wide open aperture that causes shallow depth of field.
Use color.
Use human interest.
How to see figure to ground separation.
If you are trying to choose the best photo out of a set, the counsel is typically to look at thumbnails. This is, in part, because you will be able to easily see the best figure to ground separation. Look at this collection of thumbnails. Can you choose a couple of pictures where the subject is clear? Are there some pictures where you have no idea what the subject is?
Other techniques include taking off your glasses when you are looking at pictures, put tracing paper on top of prints, or choosing a blur filter in your post processing software. When you are out shooting, try to visualize in B&W.
Exercise
Look through a collection of your images. Can you find ones that have good figure to ground separation? What compositional tool did you use to get the separation?