1. Listen to the Gentiles(The first may seem a bit obscure, but Krugman indicates that he means "Pay attention to what intelligent people are saying, even if they do not have your customs or speak your analytical language." )
2. Question the question
3. Dare to be silly
4. Simplify, simplify
PS: If you'd like an example of Krugman's most speculative work in trade theory, here's his paper on The Theory of Interstellar Trade.