1. Modal verb for advice: "should be" in "The message should be straightforward" is used to give advice or express necessity, which is a common and natural way to make recommendations in spoken English.
2. Conditional sentence: "If an ad is too complicated or vague, it loses its effectiveness..." is a first conditional sentence, showing the result of a possible situation, which adds complexity and clarity to your answer.
3. Present simple tense: The answer uses present simple tense throughout ("clarity is crucial", "ads use simple, direct language") to talk about general truths and habits, which is appropriate for this kind of discussion.
4. Infinitive of purpose: "to get their point across quickly" uses the infinitive form to explain the purpose of using simple language and visuals, which is a useful structure for IELTS answers.