Tim Keller discusses 3 rules for Gospel Polemics in his new post that "will help us neither avoid polemics nor engage in them in a spiritually destructive way." Here are the rules, but go read his explanations.
1. Carson’s Rule – You don’t have to follow Matthew 18 before publishing polemics
2. Murray’s Rule – You must take full responsibility for even unwitting misrepresentation of someone’s views
3. Alexander’s Rule – Never attribute an opinion to your opponent that he himself does not own