What does an advertising copywriter need to know?
To begin with, a little of everything. If you can write interestingly and with freshness and insight in a related field, you can learn to apply that writing skill in a business situation. Where many copywriters (and art directors, etc.) are lacking is in the business aspect. Pretty quickly it become apparent whether the copywriter really cares about selling. Your writing needs to speak to the real needs and emotions of the people who buy what the agency’s clients are selling. That’s true whether you’re selling soap to the masses, or multimillion-dollar TV transmitters to a small number of engineers. You need to know your market, and be able to talk with them as if you were talking to them personally. It’s still true that “advertising is salesmanship in print.” Some of that you can learn in school. Some of it can’t be taught anywhere.