Silhouettes don’t have to be black cutouts in side view seen against a white background. All shapes present silhouettes, and vision researchers have shown that one of the first tasks of perception is to be able to sort out the silhouette shapes of each of the elements in the scene.
A good rule of thumb is that the most important part of the pose, often the hands or the face, should be brought into the silhouette, rather than embedded inside the pose. In the painting "Forge of Vulcan" by Velasquez, the sun-god Apollo has arrived at the Cyclops' forge to break some bad news to Vulcan. The artist has made sure to bring Apollo's upraised finger into the silhouette to make it clear that he is relating a narrative.
Silhouettes can have dramatic, unexpected shapes, like the wind-blown cape of the pirate Billy Bones by N.C. Wyeth. Only the hat, the tip of the elbow, and the end of the spyglass break the outside shape, literally concealing the hand of the pirate, and making his intentions seem more mysterious.
Try to imagine the poses of your important figures converted into a simple silhouette, either black against white or white against black. If the shape standing alone still conveys the action, it will probably work fully painted, too.
The most important element of the pose should be placed with the strongest contrast against the background. The background can be designed so that it gradates up to a bright halo behind that element, while the other parts of the silhouette can be left a bit closer in value. In this N.C. Wyeth painting, the head is the featured part of the silhouette.
In this little sketch of a fellow artist that I did during a figure group, I chose to lighten the background behind her hand, rather than behind her head, because I thought it was more important.
Related posts: Edge Induction, link. Flagging the Head, link.