When eating with chopsticks, do not leave the chopsticks in the rice bowl at the end of your meal. This resembles the incense sticks used to commemorate a death and is considered insulting. Place the used chopsticks side by side either on the table or more commonly, on top of the bowl.
Do not tap the edge of your rice bowl with your chopsticks: The older beleive that if you do such thing, next life you will not have enough rice to eat ( But in fact, because tapping chopsticks to the bowl will cause chipping to the bowl hence dangerous if you swallow it accidental when eating your rice - )
Do finish until last grain of rice in the bowl. Sometime you can see people hold the chopsticks ( lay the chopsticks paraleil to the ground) and slightly bowed. That' s the gesture to thank God - Heaven and Earth - and people who work hard to produce the grain of rice to feed them.
If you are invite to a family meal, wait until the oldest member of the family eat, then you can follow after that: That' s the gesture to show your respect to them. And eat all things they put into your bowl: Your host chose the best bit to his/her guest. Is you had enough food , slightly cover your hand over your bowl and refuse politely and they will ( hopefully) stop adding food into your bowl.
If you are happy with the services provided by your local staff as a guides and drivers.. a tip is appropriate. While it may not be customary to you, tipping inspires great service, and is an entrenched feature of the tourism industry across Vietnam destinations. As a general guide on private tours, please allow 3USD to 5USD per day per traveller for each of your local guide and driver. Of course you are free to tip more or less as you see fit, depending on your perception of service quality and the length of your trip