Like many problems in self improvement I think this comes down to a two essential factors, Practice and Evaluation. Social activities like convincing people need extensive real world practice to effectively apply, even with the best advice. However, improvement can only be made if you know how effective you are actions are.

that much is obvious

As an initial suggestion: locate only groups on difficult but none controversial topics and practice convincing people of things, asking them to rate their knowledge, opinions and beliefs before and after

perhaps we could set up such a thing here on less wrong for people to practice on one another or does that seem to Dark arts to people?