Choose the right location. A formal debate should take in the appropriate setting. For example, an academic debate is best conducted in a classroom.
Open broadly. While your debate has a main argument, there are also side factors to consider. For example, assume you want to convince someone that the death penalty is unnecessary. You can mention contributing issues, such as its approval level in the industrialized world, or perhaps use philosophy, such as like Gandhi's quote, "An eye for an eye only ends up making the whole world blind." Inversely, if you support the death penalty, you can talk about the atrocity of murder, or mention some notorious criminals who, in your opinion, rightfully received the death penalty.
Use relevant framing. There are many ways to improperly frame or lend context to an argument. An example of improper framing would be to link the opposing side to some kind of extremist faction. For instance, if you are arguing against universal health care, associating it with communism is inaccurate and deceptive. Similarly, if you support universal health care, linking your opponent to certain conservative extremists serves no purpose other than to unfairly destroy credibility.
Know your audience. Just like there are many different debate topics, there are also many different people to listen to those topics. If your audience mostly does not favor your opinion, frame the debate with tact and professionalism. Avoid things like condescension, sarcasm or personal attacks. Also, refrain from using literary devices, such as metaphors. Although such methods are common in political debates, all debates should ideally be about the facts, not the spins you use to present them.