Coca Cola is legendary. Harley Davidson is a cult. Apple is Innovation and Mountain Dew is an adventure. To develop an iconic brand like them, just a conscious effort is not enough, because it is quite difficult to remain an icon with brand following for a long time. For example, the characteristics that baby boomers liked is not so common to what "Generation Y" likes, even though both seems to be rebels and iconoclasts in nature. So, normally the icons create a myth around them and generate enthusiasm and develop underlying curiosity about them. They speak more for the young and target contradictions. They do have a mass audience.
What will an icon ask an advertising agency to do for them?
Penetrate with repetitive legends, Make the message short and simple, try to be a little bit of contradiction, build curiosity around taglines, myths..etc., make them irresistible by keeping the message- suave, chic and matchless.