The document outlines several conventions commonly used in billboard design including: - Using a large, bold masthead at the top to identify the product or brand. - Employing bright, complementary colors that attract attention and link to the brand. - Including a catchy strapline or slogan below the masthead that briefly summarizes the message. - Providing essential contact details like a web address at the bottom. - Centering a unique, creative image that dominates the page without clashing with the text. - Positioning text at the top and bottom around the central image.