Choose an advertisement that attracts your attention. Work from the original, not a copy. Most advertisements include pictures and words. Many also include symbols and a story line. All ads make a pitch to the consumer, making positive or negative appeals of various kinds, for example, emotional intellectual, conscious subconscious, with social trends against social trends.
Appeals can be incredibly subtle, complex, and calculated.
In this paper, just describe the ad. Notice every detail. Try not to overlook anything. Heighten your perceptions and look intently. As you record your observations, search for language which exactly captures your perceptions.