Phase 1. All parties take turns expressing their beliefs on the issue with any relevant information. No questions are asked.
Phase 2. Parties take turns asking questions about the other's specific view points on the issue. Bringing up clarification issues, external influences that may have an effect on their positions and attempting to enforce their own position.
Phase 3. All parties then end with their closing statements about their positions, any changes in opinions they may have had, and offering possible solutions to the problem.
There should be no intellectually dishonest fallacies used (No-True-Scottsman for example). No personal insults being thrown. Parties should not interrupt each other and should get Equal Time. Off topic discussions should be kept out of the issue. My greatest hated method of attack in bad debates is what I like to call the "Definition Fallacy".
The Definition Fallacy is the idea that just because a word carries a specific meaning that means no matter what outside influence happens that word carries that specific meaning with no possible way to change.
This shows up a lot in feminism where when you start to criticize the movement they don't try to debate but instead just point to the definition of feminism in the dictionary as a way to silence opponents. This implies that because feminism is defined as "The movement for equality between men and women" that any action the group takes can ONLY be for "equality".
I've also seen religious people do this in debates while trying to call up specific definitions of "Evolution" or "Faith" and using those instead of the generally accepted definitions for them because it better helps their argument.