In our long distance relationship the most important invisible rule is....Trust.
Next to that just one real simple rule....No dancing with strangers in a bar except for good friends in life. In Spain dancing tends to be something very intimate and in Brazil it's even worse:-)
Another invisible rule which works very good...bodylanguage in order to check out the mood we're in.
This makes it possible to let someone have a bad mood without bothering the other and vice versa. Leave someone to have his/her space instead of nagging every 10 minutes about someone not being cheery.