The following are some tips for person to person or telephone communications:
1) Try to give greetings in Portuguese (Bom dia, boa tarde, boa noite).
2) When speaking English, if the person is present, keep an eye out for that glazed expression that reveals lack of comprehension.
3) If on the phone, do not assume that you are being understood. Ask: "Is that clear? Do you understood?". If speaking in person, remember that nods and smiles do not always signify understanding.
4) Avoid contractions.
5) Avoid questions that can be answered in yes or no.
6) Enunciate distinctly and slowly, but not too slowly, which may be patronizing.
7) Overpunctuate with pauses and full stops.
8) If there is a way to do so, confirm in writing by telex or letter what was said as soon as possible after the meeting or conversation.
9) If possible, say numbers in both languages. If speaking in person, also write the numbers.
10) The seven deadliest sins of international misunderstanding are:
Avoid these. Be direct and simple. Take your time.
Remember: the cost of ambiguity can be steep.
Do's and Taboos Around the World: A Guide to International Behavior. Roger E. Axtell. New York: Wiley,1990. 172-173.
As Chacrinha once said: Quem nao se comunica se estrumbica! (If you don't communicate, you get scr....d!)