It's in your best interests not to drink the tap water, especially after flooding!
Dress modestly and appropriately when visiting local dwellings and religious sites, etc.
Leave your valuables behind before a night out on the town, or going to the beach.
When crossing the road, especially in Ho Chi Minh city, always keep looking to the left and right and walk slowly!
Do not offer money directly to minority people - instead donate to a local charity or offer a small gift, such as pens.
Try at least once the delicious, local street food.
Always ask permission first before taking photographs, especially in minority areas.