Things to do or not to do in Vietnam

DO

• Store your cash, credit cards, airline tickets and other valuables in a safe place. Most 4-star hotels have in-room safes, otherwise ask the reception to keep your valuable things in their deposit facility.
• Take a hotel business card from the reception desk before venturing out from your hotel. This will make your return to the hotel in a taxi or cyclo much easier.
• Carry a roll of toilet paper in your daypack on long excursions from your base hotel. You never know when you might need it!
• Dress appropriately. Not only for the prevailing weather, but also not to cause offence to the local people. Vietnamese have conservative dress codes, and it is only in larger cities that these codes are a little more relaxed. Do not wear revealing clothing.
• If invited into a home, always remove your shoes at the front door when entering.
• Ask for permission when taking a photograph of someone. If they indicate that they do not want you to, then abide by their wishes. DO NOT offer money or push the issue.
• Drink plenty of bottled water. During the summer months you should be drinking a minimum of two liters per day. If you drink tea, coffee & alcohol you should increase you water intake accordingly as these will help to dehydrate you.   

DON’T

• Never carry more money than you need when walking around the streets. Do not wear large amounts of jewelry. There are two reasons for not doing this:
  (1) It is considered impolite to flaunt wealth in public;
  (2) It is more likely that you may become a victim of a pickpocket or drive-by bag snatcher.
• Don't be paranoid about your security, just be aware of your surroundings.
• Don't wear singlets, shorts, dresses or skirts, or tops with low-neck lines and bare shoulders to Temples and Pagodas. To do this is considered extremely rude and offensive.
• Avoid giving empty water bottles, sweets and candies or pens to the local people when trekking through ethnic minority villages. You cannot guarantee that the empty bottles will be disposed of in a correct manner, and the people have no access to dental health. If you want to give pens, ask your guide to introduce you to the local teacher and donate them to the whole community.
• Never sleep or sit with the soles of your feet pointing towards the family altar when in someone’s house.
• Never lose your temper in public or when bargaining for a purchase. This is considered a serious loss of face for both parties. Always maintain a cool and happy demeanor and you will be reciprocated with the same.
• Do not try to take photographs of military installations or anything to do with the military. This can be seen as a breach of national security.
• Never take video cameras into the ethnic minority villages. They are considered to be too intrusive by the local people.

The above advice is meant to help you have a perfect trip to Vietnam. Do not be overly paranoid though. Generally, Vietnamese people are very appreciative if they see you trying to abide by the customs, and very forgiving if you get it wrong or forget. If you make the effort, you will be rewarded.

Don´t leave home without...

Following advice is collected from LonelyPlanet Guidebook
Bring as little as possible, Vietnam has pretty much anything you can find back home.
Necessary documents: your  passport and  visa (with their copies); 2 photos (3cmx4cm), tour dossier (if any) and others (if needed).
Cash in US$5’s, US$10’s, US$20’s and US$100’s (US dollars are commonly acceptable)
All the soaps and smellies are cheap and plentiful, and clothing, shoes and backpacks are all manufactured in Vietnam and available at a fraction of the price in the West. Tampons are available in all major towns and cities, but not in more remote areas.
A Swiss-army knife or equivalent come in handy, but you don’t need 27 separate functions, just one blade and an opener. A torch (flashlight) and compass are also useful.
Other handy things to bring are: name cards, as Vietnamese deal them out like a deck of cards; ear plugs to block the ever-present noise; a universal plug adaptor; a rain cover for the backpack; a sweater for the highlands and air-con bus trips; mosquito repellent to keep the bugs at bay; and a folding umbrella if you plan to visit during the rainy season (July and August are the wettest months).
Finally, the secret of successful packing:  plastic bags – not only do they keep things separate and clean, but also dry. That means a lot at the end of a long, wet day.