Travel insurance: Make sure you are fully covered for medical treatment, hospitalization and medical evacuation. Do not leave your home without any travel insurance.
Take a business card: once you arrive in your hotel, make sure to take a hotel business card. This will make your returning a lot easier.
Prepare enough water: remaining a tropical climate, Vietnamese temperature can have you sweating out a lot of fluid (especially when you are walking around). Therefore, make sure to take a couple bottles of water together wherever you go. You will be surprised that a bottle of water is more expensive than the local beer.
Dress appropriately: this concerns not only the weather, but the Vietnamese customs as well. You must be properly covered when entering churches, shrines, temples or sacred places. In addition, you should always remove your shoes when invited into a home.
Keep an eye on your valuables at all times: don't carry excessive amounts of cash. Bag snatching and pickpockets are quite common, especially in big cities such as Hanoi, Ho Chi Minh City, Da Nang...Leave valuables, important documents and the balance of your holiday cash in the hotel safe.
Ask for permission: ask people’s permission before taking a photograph of them or anything else. If they do not want you to do that, do not push the issue or offer money.
Individual security: report robberies to the police, especially when losing important documents (e.g.: passport, credit cards, etc.) or large sums of money. Police reports are needed to obtain a new passport together with Vietnamese visa. Keep a photocopy of your main passport page.
Personal belongings: do not walking around in streets with much cash or jewelry in your handbag. It’s not something to be paranoid about, simply do not make yourself be a target for pickpockets or drive-by bag snatchers in streets.
Fight with vendors: getting aggressive or losing your temper during a business negotiation is considered a serious breach of conduct. This will probably end with you whatever you were trying to buy. Don’t become mean or shout when you bargain at the market. You will be more successful if you smile more.
Take photos without permission: this mainly pertains to residents and military property. The Vietnamese government won’t take kindly to potential security breaches. In additionally, do not take pictures of anything that’s related to military unless you would like to be considered a spy.
Costumes: do not wear shorts, dresses or skirts, or tops with low-neck lines and bare shoulders when visiting Churches, Pagodas, Temples and sacred places in Vietnam. To do this is considered extremely rude and offensive.
Drug problems: do not get involved with drugs. Penalties are extremely severe in Vietnamese law. In particular, do not carry anything through customs for someone else unless you know exactly what it contains.
Security at night: do not stay out late at night in unfamiliar parts of town or in areas of Hanoi, Ho Chi Minh City, or Da Nang.