Argue your character's viewpoint as best you can. Don't assume that your opponents personally prefer their main arguments; they're in character too.
Courtesy and Open-mindedness
It's a bad idea to let an in-class debate or argument get heated for several reasons. Your school has rules restricting abusive language, and your instructor will be enforcing them. This is only a simulation; even if it weren't, people are entitled to their opinions and being rude to them won't make your opinions more attractive. You should also avoid dirty rhetorical tricks like interrupting people, speaking for longer than you need to in order to keep your opponents and critics silent, or making ad hominem attacks (against the person instead of against their idea). These tend to be poor substitutes for a carefully researched and well-thought-out argument.
Never lie in an interactive exercise. Further, be ready to back up any and all of your claims with evidence. You're simulating an important real-world event, in which experts and representatives who lie would ordinarily damage their careers and harm their causes. If you don't know something, ask around to see if one of your fellow participants does. If not, you'll just have to admit that you don't know. Likewise, if pressed, be truthful about data that undermine your position.
Careful preparation and examination of your character and of the scientific issue you're approaching will make it less likely to encounter data that weaken your arguments. Logical, well-thought-out arguments are more likely to convince others. While debating, stay on topic and seek a solution that furthers at least some of your character's goals, even if it will require a compromise.