Every element of a flash-based presentation has to be supporting each other. Texts, videos, images or animation, everything must be harmonized to highlight the core message of the presentation. And you can also pitch in your creativity to enhance the impact of your visual stuff. Again planning has to be perfect. There may be six points to increase the effect of visuals:
Visuals are a powerful medium to convey the message to the audience, but if and if they are used cautiously and in a synchronized way.