Maintaining a conversation is a lot like starting a conversation. We try to listen to what the other person is saying, stay on topic, and ask open ended questions (who, what, when, where, why, and how questions). The difference is that we take turns with the other person (or people) and do this several times in a row. One good idea is when someone asks you a question give a short answer and then to ask them the same question. Your goal is to ask questions that
For example if a person asked you "What's up"?
You would give a short answer like, "Not much," or "Just studying for my English test". Then follow up with a question, such as "What's up with you?"
Then you listen to the person's answer and try to ask a question about it. If that doesn't work, move on to another question like "How was your weekend?," "Are you going to the game Friday night?", or "I'm a little nervous about the homework for English. How did it go for you?"