1. Store your cash, credit cards, airline tickets, passport and other valuables in hotel’s safety box. Carry a copy of your passport with you at all time.
2. You must keep the yellow immigration slip with your passport in order to get out of the country.
3. Take the hotel business card before venturing out from your hotel.
4. Take lots of USD 1 and small amount of USD 5 or USD 10 or change your currency into VND. It will be useful for paying the taxi driver, in the market.
5. Make sure that the Vietnamese notes you receive are not torn.
6. Always take a taxi with the logo on the car, agree on the price upfront and prepare information of the place in writing.
7. Have your pictures developed in Vietnam. It is really cheap.
8. Carry a roll of toilet paper in your day pack on long excursion from your base hotel.
9. Bargain, bargain and bargain. Very few stores have fixed priced or any thing that is unique. Do not be afraid to be firm about your top price and walk away. You will find the item at some places else if the vendor does not meet your price.
10. Ask for permission when taking a photograph of someone or in certain places.

 
Source:   www.vietnamtourism.com