Hi Kibbutz. It's been so long. Here's a link that you can check which is an excerpt from the UN Charter a provision that is generally about the General Assembly - http://www.un.org/en/documents/charter/chapter4.shtml. This link tells about the agenda building and scope of issues being dealt with at the General Assembly.But I believe that what determines the order that the world leaders speak in the General Assembly is the urgency of an issue specifically if it involves the matter of peace and security, or anything that involves a bigger scope of the world like wars/disputes, armaments and disarmaments, economic and global warming.These are just some of what they have been discussing thoroughly nowadays if you will notice the behavior of their talks.They're like trying to reach out for resolutions as leaders narrow down proposals in order for them to make few nominations to be voted upon. But sometimes, there is what we call power resolution or manipulation behind as always I guess.