When writing an advertising essay, it's important to focus on supporting an opinion about one of its aspects rather than only describing something in the history of the industry. While history and descriptions of ads may usually be acceptable in an essay on advertising, what really counts, as in any essay unless the specific instructions say otherwise, is to make a thesis statement in the introduction, support it in the body and sum it up in the conclusion. If the specific topic isn't given, it can be best to pick a controversial one such as the effects of advertising on children.
A controversial topic is exciting because it can typically be well-argued on both sides. The key is to choose one stance, or thesis, in an advertising essay, yet also include the arguments that support the opposite viewpoint. It's crucial to then discuss those arguments and point out any strong points, yet how even they weaken in comparison to the ones that support your stance on an advertising issue. For example if your thesis in your introduction is that advertising isn't really harmful to children, you could mention that society being concerned about the well being of kids is always important, but that statistics don't show that advertising is of significant harm to young people.
Without citing the actual statistics to prove your claim though, the essay won't be effective. You should, whenever possible, cite the name and date of each study as well as use the exact numbers or results to back up your supporting arguments. This type of evidence or proof is different than general information about the history or scope which doesn't support your thesis argument. While general background information and historical or case references do enrich your work, it's the statistics and evidence used to back up your thesis statement that are likely to earn you strong marks on an advertising essay.
Unless the instructor indicates otherwise, each body paragraph in the essay should concentrate on one supporting point to the thesis. All of the sentences in the paragraph should be on that topic and that particular point. The sentences should expand on the point while still convincing the reader of the thesis.
A great tip to remember, if writing an advertising essay becomes difficult, is to always look back at your thesis statement in the opening paragraph to keep you on track in supporting and proving it. Persuasion is important in both advertising itself and on essays on the topic. Without being focused on convincing the reader of your thesis, your grade on the essay is likely to be mediocre.