1. When crossing the street, do not change your speed of pace, do not run, do not step backward.
2. Do not drink tap water. Make sure to drink plenty of bottled water.
3. Do not wear large amounts of jewelry and never carry more money than you need when walking on the street.
4. Do not exchange too much money at one time, as you will end up with a large wad of notes.
5. Don’t wear singlet, shorts, dresses or skirts, or top with low - neck lines and bare shoulder to temples and pagodas.
6. Never sleep or sit with the soles of your feet pointing towards the family altar when in someone’s house.
7. Nerve lose your temper in public or when bargaining for a purchase.
8. Always maintain a cool and happy demeanor and you will be reciprocated with the same.

 
Source:  www.vietnamtourism.com