The dog might look friendly, but if you don't know the dog, there is no way to tell how it reacts to strangers. If the owner gives you special instructions that differ to the ones told here, follow them. If the owner lets you pet the dog, ask the owner where the dog likes to be petted. If you see a dog with no owner loose on the street, proceed carefully and stay in position to defend yourself if necessary. Dogs chained up or left in a yard or other location with limited space may be more likely to bite, as are dogs eating or chewing on something. Approach these dogs with caution, and abandon attempts to pet them at any sign of aggression, as described below. Signs of aggression include barking, a tail standing straight up, raised hackles, growling, or a body held in a rigid position. Signs of discomfort, fear, or anxiety include lip licking, showing the whites of the dog's eyes, avoiding eye contact, holding the tail low, yawning, or pulling the ears back. Never stare into a dog's eyes, that usually makes them think you want to fight them. If the dog does not calm down or approach you within thirty seconds, abandon the attempt. Invite the dog to take the first step by squatting down closer to their level. More confident dogs only require bending over slightly, but don't bend directly over the dog, as this could make them feel threatened.  Sometimes, you can help a dog to calm down by introducing yourself. Dogs introduce themselves to each other by sniffing. Humans introduce themselves to each other by shaking hands. This works with a human introducing themselves to the dog. The human holds out the back of their hand to the dog’s snout, and if it sniffs the hand, it will usually calm down. Never squat down near a dog without an owner or a dog that is acting aggressive (see the signs listed above). Remain standing to defend yourself in case the dog attacks. If squatting down still hasn't attracted the dog, and it is acting shy or skittish (running away or hiding), look away since eye contact can be...

TL;DR in Vietnamese:
Xin phép người chủ để âu yếm chú cún. Cẩn thận với những chú chó không có chủ. Lùi lại khi thấy chó có dấu hiệu gây hấn hoặc không thoải mái. Cúi xuống hoặc ngồi xổm để khuyến khích chó đến gần. Dỗ dành chú chó có vẻ nhút nhát tiến lại gần hơn. Đưa nắm tay ra. Quan sát tâm trạng thoải mái của chú cún.