There are hardly any special rules to get Portuguese people to like you - just be polite and rather reserved, the “too much” attitude isn’t appreciated.
The Portuguese are typically gentle, friendly and modest - try to be like them. Visitors who make the effort to learn even a few simple words or phrases such as hello (bom dia), thank you (obrigado) and goodbye (tchau) will be appreciated as well.
The Portuguese are also concerned with appearances and with respectability. Being smartly dressed, whatever the occasion, is seen as a mark of respectability, especially amongst the older generation.
Displays of public affection and emotion in public are acceptable but don’t go overboard (for example, screaming at your child on the street isn’t a good idea).