Depending on the subject of your speech, one way to organize your group presentation is to divide it by topic. For example, a proposal for the improvement of a public space might a divided so that each presenter discusses one of the alternatives. A class group presenting a discussion of the Battle of Gettysburg might divide the presentation so that each speaker discusses one of the major events of the battle.
If the topic lends itself to it, a chronological approach can be effective. Each speaker is assigned a particular time period, such as 1970 to 1980, or it might simply divide the topic into past, present and future. For example, a group of three people discussing the fiscal history of a business might divide it into past performance, present circumstances and future projections.
It is important when planning your group's speech and presentation that you choose and overall leader because someone has to make sure each group member is doing her part. In business, choosing a leader is often done by the boss who gives you the assignment. In other situations, such as a classroom, take a vote or draw straws.
There is more to being prepared for a presentation than just having things organized and planned. You also need to be confident when you are speaking. Practice your presentation and the process of passing off to the next person in your group until it becomes second nature.