Students who use evidence well get high grades. Those who don't, unfortunately, don't. You probably will know that there's weak and strong evidence. And weak evidence won't convince your instructor either. She or he also wants you to consider and comment upon evidence that doesn't support your case, just as a skilled defence lawyer will try to poke holes in the case being presented by the prosecuting lawyer.
Facts are very strong evidence.
They can never prove an opinion, but they can provide vigorous support. Lawyers spend years perfecting their techniques in presenting evidence effectively. You don't have years to perfect your technique, and hopefully this pamphlet will teach you a few shortcuts, but don't expect skill in this technique to develop immediately or without effort and attention on your part. But following a few simple but important steps will ensure you start off in the right way. They often look nervously around to see what others are doing with their napkins, etc.