First of all, be prepared for changes. Circumstances change and speakers might not be available at all any more or only at certain times. Other speakers might be able to fill existing gaps.

Required information

To be able to plan the schedule you need the following information:

Once you have that and a sufficient number of presentations has been confirmed, you can start planning. At least two third of the available slots should be covered.

Rules

A number of rules apply. Some of these simply cannot be ignored, some need be followed for a decent result, and some might be broken under certain circumstances. The rules are listed with decreasing priority.