You need to be aware that they will occur. You didn't get the assignment read, and you are worried about what the professor will think. You can still participate in discussion, but by making connections between what students are saying and what the group read earlier. Or you can express an opinion about the materials, but be honest about not having read them. Another student monopolizes the discussion.
Some students just love to hear themselves talk.
You may not see this as a problem because it means you don't have to talk as much in class. But, this kind of student does everyone a disservice, because you and other students may not get to have your ideas aired or questions answered. Try to encourage non-talkers to talk. Try to remain professional and respectful at all times. Refrain from negative approaches.