The Portuguese are remarkable people, who also happen NOT to be Spanish. Don't confuse that simple fact, follow these tips, and you'll be fine:

• Greeting people here is slightly different to neighboring Spain, and a bit confusing. So we'll tell you this: always extend your hand to shake the hand of the person you are greeting. If it is a woman, presume that you will kiss her cheek, but wait until she offers.
• Do not yawn or stretch in public; it's considered extremely disrespectful and will garner glares from onlookers.
• Never eat with your fingers or lick them no matter how tasty that sauce is. This rule changes slightly only if everyone else is doing so—which is extremely rare.