In a silhouette, the main subject’s colour and surface texture recede. Shape, posture and relationship to a brighter setting remain. An interesting subject is therefore not automatically a good silhouette. A person facing forward with arms close to the body may become an indistinct dark mass; a slight turn or clear space between arm and body makes the pose readable.
Find a bright background
An evening sky is only one option. A bright window, fog or illuminated wall can also work. Position the subject so its decisive outlines fall against a quiet brighter area. A dark tree directly behind the head merges with it even if the rest of the sky is ideal.
A lower camera position may separate feet or objects from the horizon. Check whether the new angle creates unwanted overlaps, however. With several people, heads and bodies should not merge accidentally. Small gaps often matter more in the finished image than facial expression, which will not be visible anyway.
Think about exposure and focus separately
Expose so the bright background retains the detail and colour you want. Depending on metering, negative compensation may be needed. Still focus on the dark main subject or its clear edge. The brightest area is not automatically the correct focus plane. A test frame reveals whether the outline is sharp and the shadow sufficiently dark.
Disable automatic fill flash if it reveals the silhouette unintentionally. Not every subject needs to become completely black. A little remaining texture may suit the image as long as the shape is clear. You can deepen shadows selectively during editing, but inspect fine hair, branches and narrow gaps.
Select the decisive moment
During movement, readability changes from frame to frame. A runner is often clearer when arms and legs separate. Take a short sequence and choose by outline rather than only the strongest sky colour. Leave enough room in the direction of gaze or movement. A dark outline near an edge can be compelling, but should not be accidentally clipped.
