Successful teams will adopt a division of labor that plays to their strengths. The first debater of each group will have ample time to prepare a well thought out presentation. The second debater, and especially the third, will have to think on their feet to refute and respond to the opposition's arguments, claims, and evidence on short notice. The division of labor you adopt will also play an instrumental role in how effectively you prepare for the debate. Remember that most of the real work will take place prior to the debate while you are researching, holding mock debates amongst the members of your own group, and writing responses.
Careful preparation is essential to effective presentation.