Experiments in participatory and deliberative democracy, creativity, and collective intelligence show that high-quality deliberation requires at least the following seven ingredients:

Participants should be engaged through a “T-shaped” approach that combines deep technical expertise with a wide range of user perspectives.
Relevant public authorities should be closely involved and make a clear commitment as to how they treat the outputs of the process. The higher up they go on Sherry Arnstein’s participation ladder, the more likely they are to generate interest and a positive outcome.
Participants need to be given access to reasonably accurate information that they believe to be relevant to the issue.
Participants should represent the diversity of positions in the public. The benefits of cognitive diversity and the legitimacy of the process are best ensured by a sufficiently large — and, if possible, truly representative — sample of a given population.
Arguments offered by one side should be answered by considerations offered by those who hold other perspectives.
Participants should be allowed to sincerely weigh the merits of the arguments, and arguments offered by all participants should be considered on the merits, regardless of which participants offer them.
The process should be transparent, through the media and on- and offline interaction with a wider public, in order to increase the legitimacy of the solutions proposed and to tap into wider cognitive diversity.