Off the beach and outside of big city nightclubs, avoid short shorts and tops that reveal cleavage.
Dress well when visiting pagoda. Knees and shoulders should be covered.
Keep your cash, card and valuable in a secure hotel safe.
Try to take taxies that are part of large, reputable taxi chains.
Travel with recommended tour agencies. A good resource is Lonely Planet and Tripadvisor.
Remember to take some name cards from your hotel when you go out. Pronouncing Vietnamese words is tricky.
In markets and less fancy shops, it is fine to bargain.
While violent crime is very rare in Vietnam, bag snatching is a problem. Carry a backpack or a bag that wraps around your torso.
Do not wear expensive necklaces
Do not go overboard with public displays of affection. Holding hands is fine.
Do not dart across the street. Walk slowly and steadily, trying to make no sudden movements.
Do not go window shopping in the early morning. A shop’s first customer is thought to set the tone for the day. If you go in, ask price or try on and do not buy, the vendor will not be happy.