The Vietnamese family unit (particularly in the rural areas) is patriarchal in nature with strong familial ties. It is not unusual to find three or four generations living in the same household. Personal names are written with the family name first, middle name second, and the first name last. It is common practice to address people by their first names, it's not so common addressing people by the last name.
Observing the following local customs will help keep us from embarrassing ourselves with the local. Crossing the index and middle fingers is considered to be a lewd gesture. Touching someone, especially on the head, is not welcomed. Motioning for someone to come with your palm up is considered rude. The Vietnamese would do this only to younger people with the palm down. And, last but not least, the Vietnamese (like most other Asians) do not like to lose face. When they don't understand a request or question, they will still respond affirmatively or give a smile so as not to lose face. Although they might disagree, they will nod affirmatively to avoid confrontation. The Vietnamese are not prone to show their emotions in public.
Dressing should be cared about while in Vietnam. At temples, pagodas, mausoleums...and other sacred places, it's strongly recommended (although not always compulsory) the visitor dressed properly with long pants and collared-shirt. At meetings, the host would feel much respected if the guest is dressed properly. Dressing properly would make the procedures/formalities with the authority much smoother. The Vietnamese cares about dressing, but they are not too strict about it. Probably this is due to the warm weather in Vietnam. Local people would tend to get dressed in a sensible and proper way. The guests don't always have to be contained in suites...in the summer. There's no nude or topless beaches in Vietnam. Women should not wear clothes that show too much skin in the public, they may get bad sunburns sometimes. But nowadays things are changing and there seems to be a trend even among the Vietnamese young girls about being trendy hot. Many young boys would welcome this though.