Focus on an external incident that will affect the characters. This can be a physical reaction to a character or purely environmental changes.
Example from Literature
On sultry summer days at my grandma’s farm in Michigan, the air gets damp and heavy. Storm clouds drift low over the fields. Birds fly close to the ground. The clouds glow for an instant with a sharp, crackling light, and then a roaring, low, tumbling sound of thunder makes the windows shudder in their panes.— Patricia Polacco, Thunder Cake