After four months of interactions between Mr. Trump and his counterparts, foreign officials and their Washington consultants say certain rules have emerged:

Keep it short — no 30-minute monologue for a 30-second attention span.

Do not assume he knows the history of the country or its major points of contention.

Compliment him on his Electoral College victory.

Contrast him favorably with President Barack Obama.

Do not get hung up on whatever was said during the campaign.

Stay in regular touch.

Do not go in with a shopping list but bring some sort of deal he can call a victory.