Debate and discussion are two of the most important activities that students of history engage in. We refine our understanding, process information, and learn to grapple with ideas that we didn't develop, and may not agree with. Thus, it is wise to approach a debate or discussion with a few things in mind.
Study. Take notes, watch videos, and read books. That's where the knowledge is.
Do not come to a debate or discussion without preparation. If you are tasked with debating, whether it's the side you agree with or the side that you don't, ensure that you do the research due to the subject. Understand both points of view, not your own, and you will be well on your way to defeating your opponent. Search for relevant and important statistics, yes, but also ensure that you understand the structures of logic that you use to defend and attack certain points. Ensure your data comes from reputable sources, as a credibility attack can be gruesome.
Whether your goal is to defeat an opponent or to gain better understanding, respect is the most important single point to remember. You must respect both the subject and the participants. Respecting the subject includes spending the time you should to understand it (see preparation), and respecting the participants means remaining calm, refraining from ad hominem attacks, and listening. Without actual active listening to your opponent, you're either focusing on the next point you're going to make, or the ways that you could counter the words they're actively saying. You aren't focusing on what's actually being said, and without that knowledge you cannot effectively continue to participate.
Avoid logical fallacies at all costs. They are lazy, sloppy, and often are a sign that the speaker is either not prepared or not confident enough to really participate.
Debate vs. Discussion
Debates are structured to allow participants to definitively prove a point, and discussions are designed to enable students to posit theories and then have those theories refined, redesigned, or otherwise altered by the group. Both have their merit, but do not try to please everyone in a debate, and do not try to attack and destroy other discussion participants.