Controlling Conversations

As of right now, I will be trying to find information in field and from other sources on how to control a conversation. As a conversation begins I notice that I have a lot of control, but as it progresses I begin to realize that the control I have starts to wane. What I am looking for is some ways in which I can keep the control. It is not so much control even, I just don't want to be the guy on the side who just laughs and listens as the conversation continues.