Travel, Teach, Live in Europe and Middle East
Try to speak the language. Any attempt to speak Portuguese will be seen as a respectful attempt to fit into their culture. Even if you don't do a very good job, the Portugal natives will be very happy to help you communicate once they see that you've tried to do so on their terms.
Wear appropriate clothing when visiting any of the several religious monuments within Portugal. You don't have to dress up, but don't go in wearing shorts or just your swimsuit. Long pants and sleeves are the most respectful attire.
Be respectful of the geography. Many foreigners mistakenly believe that Portugal is a part of Spain, which it is not. The Portuguese people find this assumption highly offensive, so get your facts straight before discussing this topic.
Expect the people of Portugal to speak loudly and quickly. This does not generally indicate anger or any other negative emotion, it's just the way they speak.
Relax your sense of time while in Portugal. Things will get done in good time is the way to behave in Portugal, so don't sweat it if you're running a little late for an appointment or a social date, and don't expect everyone you socialize with to be punctual either.
Kiss your friends, family and acquaintances on both cheeks. Touching is common in Portugal, so relax and accept the friendly hugs, pats on the back, kisses and hand holding that comes naturally to these affectionate people.
Instruct your children to avoid eye contact with adults. Portuguese children avoid eye contact with their elders our of respect, and direct eye contact is considered quite rude.
Resist the urge to step back from someone as they talk to you. In Portugal, personal space is considerably less important than in the U.S., and most people will consider you quite rude if you back away. At the very least, they will step forward again, so you'll wind up in a rather comical-looking chase down the street as you attempt to have a conversation.
Get used to being interrupted. Americans expect people to take turns speaking, but this isn't they way they behave in Portugal. It's common for people to speak simultaneously, and no one is offended, so just try to keep up if you feel you can't get a word in edgewise because it probably just means like they you.
When in doubt, use the formal case of address until your new friend begins to use the informal address with you.
Avoiding politically charged conversation is always a good idea in any culture. In Portugal you should be especially careful when discussing the Galician or Olivença issues, since these can be especially heated.