For this task consult The Owl on using evidence
Also consider Aristotles' Logos and Ethos.
As in much scholarly and academic writing, you should aim for neutrality of language, avoiding emotional appeals and opinions.
A Summary of Aristotle's Appeals . . .
The goal of argumentative writing is to persuade your audience that your ideas are valid, or more valid than someone else's. The Greek philosopher Aristotle divided the means of persuasion, appeals, into three categories--Logos, Ethos, Pathos.
Logos (Logic) means persuading by the use of reasoning. This is a very important technique in academic writing, and Aristotle's favorite. Consider both deductive and inductive reasoning, and what makes an effective, persuasive reason to back up your claims. Giving reasons is the heart of argumentation, and cannot be emphasized enough. What types of support can you use to substantiate your thesis, and what are some of the common logical fallacies, that you should avoid in your writing?
Ethos (Credibility), or ethical appeal, means convincing by the character of the author. We tend to believe people whom we respect. One of the central problems of argumentation is to project an impression to the reader that you are someone worth listening to, in other words making yourself as author into an authority on the subject of the paper, as well as someone who is likable and worthy of respect.
Pathos (Emotion) means persuading by appealing to the reader's emotions. We can look at texts ranging from classic essays to contemporary advertisements to see how pathos, emotional appeals, are used to persuade. Language choice affects the audience's emotional response, and emotional appeal can effectively be used to enhance an argument.