It depends on what you are arguing, but you will always need a grabber to get someone's attention. A question,fact,or thoughtful beginning will be a good start. If you were arguing about how students should have a different dress code, you could say,"Have you ever found a great outifit that looks great, but with disappointment realized the strict dress code prevented you from wearing it?" With an argumentative paper, it is good to introduce the problem and argue how it can change in the later paragraphs :)