General rules for speaking within a group

• If you want to put in your two cents on a matter and fit into a conversation that's already happening, make sure you can jump in with a full, uninterrupted sentence. This will help you assert yourself. If you feel someone will cut you off, don't start just yet, and don't cut anyone off in the middle of a sentence.
• Treat each individual as an equal. Easy ways to do that are to refer to each person by their name and look the person you're talking to in the eyes. 
• Emphasize your similarities with other members of the group to create empathy. This can be as easy as casually throwing in the sentence how you're both vegan or like a certain TV show. Everything works as long as it is related to the conversation. 
• If someone picks up some friendly banter with you, make sure you answer at the same level. If they commented on your shirt, comment on their pants, not their weight. If you don't want to banter back, you can playfully act offended with a big smile. When you laugh it off, it conveys confidence.

How to navigate a one-on-one debate

• Sit in a comfortable and relaxed pose to signal to your brain that you are safe and there's no need to feel attacked. 
• Hold a few seconds before answering any argument or question. This will assert confidence and give you a brief moment to remain calm and answer in a civilized, friendly manner.
• Don't ridicule the other person's ideas, even if they do the same to you. Choose to be wise over being right. 
• After you've made sure to understand them, you need to make sure that they understand you. The key to good communication is speaking at eye level. If you feel misunderstood, you can say, "When I said... what do you think that I meant?"
• Know your arguments inside and out, so you know when you can agree with the other side.

• Recognize when people are getting emotional and don't play along. You are searching for a concrete point, an argument, not a feeling. A concise argument needs more than emotion to be valid. 

• Don't talk about abstract ideas and encourage the other participant to do so as well. Focus on specific examples. If someone talks about "the institution," "the industry," or other abstract bodies and ideas, ask them to refer to a specific notion or person. 

If things get heated among friends, here's how to handle it

• If someone is personally making negative comments about you, non-verbal signals are a graceful reaction. Either stare deeply into their eyes while they speak to make them uncomfortable, or just ignore them entirely and shift your energy towards the rest of the group. Prolonged silence will also invoke a sense of embarrassment in people who speak negatively of you.
• Detach your ego from personal attacks. Waste no mental energy on protecting your ego. That will allow you to be wittier in the face of criticism. You can turn an insult into banter with a joke, or you can turn it into praise for yourself if you're good at improvising. 
• If the conversation becomes heated and someone latches out on you, shooting accusations, try to slow down the conversation while they are accelerating it. One way to do this is to go over each accusation slowly together and ask them to repeat previous statements. Then, answer each question, remark, and concert individually.

• If someone is teasing you and you'd like them so stop, remain collected and friendly, and casually say that you didn't like that comment made on you. This can make people uncomfortable, and you can shake that off with a joke or a laugh. In short: calmly state what you didn't like. Once the message is received, move past it.

• If you feel that someone is crossing a line or teasing you, intending to pick a fight, set a boundary. Now, a boundary is not an ultimatum, it is presenting to the other side how you will behave in reaction to someone doing something. For example, "If you keep using that demeaning tone, I will walk away." This is for extreme cases only that will probably not occur amongst friends. Calmly state your boundary and why it is important to you. If they continue to cross your boundaries, act on your promises.

Source: CharismaOnCommand