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.

“If you were prepping people for Donald Trump, the two or three points would be: one, bear in mind this is still a guy who focuses on wins,” Peter Westmacott, a former British ambassador to the United States, said. “He likes to have wins for America and wins for himself from bilateral meetings.”

“Secondly,” he continued, “he is a deal maker, a pragmatist. Third, this is a guy with a limited attention span. He absolutely won’t want to listen to visitors droning on for a half-hour — or longer if they need an interpreter.”