Always remove your shoes, socks and hat and wear conservative dress, which should wholly cover your arms and legs, prior to entering a temple or home in Vietnam. Also be aware that it is considered rude to show the bottom of your feet toward a Buddha image or your host, which can most easily be accomplished by sitting cross-legged. 

Never point at a person, or touch their heads. In general the people of Vietnam are not used to being touched by strangers, so tapping, hugging or putting your arm around someone is likely to regarded as a violation and cause unintended offence.  

The traditional greeting amongst the Vietnamese is to bow to each other, but in modern times handshaking is common between men. A man should only shake hands with a woman if she proffers her hand first. In general, foreign men should be very careful about touching local women, as this is not customary and can easily be misunderstood. It is not the practise in Vietnam, especially for women, to touch a monk, or even their robes. 

Do not point at things, especially religious objects. If you need to attract attention, motion with the palm of your hand. It is a common gesture in many societies to affectionately ruffle the hair of children, but the head is considered sacred in Vietnamese society and such gestures will not have the intended effect. 

Avoid political comment and criticism. 

Visitors to Vietnam should be aware that it is highly likely that they will witness attitudes towards animals, which may distress, and prepare themselves in advance to deal with these matters with calm and sometimes considerable restraint. 

Overt public displays of affection between couples is frowned upon, particularly in traditional areas, and shows disrespect to the native culture. 

Tipping for services in Vietnam is in general unnecessary but will be accepted by Taxi drivers, tour guides, restaurant and hotel staff.   

When dining, Chopsticks should be used only for eating and never employed as a means of gesturing, drumming or placing in your hair. When you have finished your meal place the implements together level across the top rather than leaning into the bowl, and on no account leave the chopsticks pointing straight up as this is traditionally interpreted as a curse or omen of death. 

Sticky rice is often eaten with the hand, for which the right hand only should be used. Despite the instinct, you should never lick your fingers afterwards. If using a toothpick, it is polite to cover your mouth with your hand.