To people visiting here from abroad, especially western countries, the roads in Vietnam can seem absolutely insane. In many ways they are insane but yet there is a real system to it and I haven't really seen very many accidents or even heard of someone getting horribly hurt because of road chaos. For the visitor, the roads here appear hectic and they are, but there is a real system to it and in the end it really just kind of works.
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number 1: Forget everything you know about road rules
In the west, particularly in places like USA, Canada, Australia, and the U.K. we have a tremendous amount of rules that apply to the roadways. Some would argue that this makes the roads safer and that is probably true. Others would argue that this makes driving a nuisance and that is probably true as well. Either way, take all of that knowledge about the way the road is "supposed to work" and throw it out the window.
The Vietnamese have their own way of doing things and a lot of it isn't actually the official rules. You need to be aware of things coming at you from all angles at all times when on a bike here. In many ways I think this keeps individual drivers more aware of their surroundings and you don't hear stories of people falling asleep at the wheel very often as a result. Remember highways in USA if you are from there? Well there were times with my cruise control switched on that I very nearly fell asleep at the wheel many times. That won't happen here. Vietnam roads are like a video game where you have to keep your head on a swivel at all times.
Number 2: They drive on the right
For much of the world the road rules dictate driving on the left. I've met a lot of patriotic people that seem to think the left is the "correct" side of the road to drive on. For me, I don't think it really matters and it was just an arbitrary decision made a long time ago and it isn't going to change. While driving on the incorrect side of the road briefly in order to merge with the correct side is tolerated to some degree, just remember, the legal side of the road in Vietnam is on the right-hand side
Number 3: Use your horn frequently
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In Vietnam, hearing horns beeping all the time is extremely common. Where I come from the horn is used to let your friend know you are at his house and he needs to come outside and get in the car, or it is used as an audible middle finger to someone that did something stupid in traffic. Here in Vietnam the horn is used to let people be aware of your presence and be aware of you, or to get out of the way. It isn't an aggressive thing at all for the most part.
If you are on the main road and see a car approaching from an adjoining road, beep your horn to let them know you are there. Also, you should probably prepare yourself for them joining the road anyway and make preparations to get out of the way for them. Always use your horn when approaching intersections because I have been in this country for year and have never seen a stop-sign. The horn serves as your "hey! I'm getting close to the intersection and intend to cross through it!" warning system to all others that are approaching the same intersection. Keep your ears open to listen for others that are doing the same thing.
Number 4: Go with the flow and use others as "shields"
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As crazy as this notion might sound it is actually a very effective one, especially at massive intersections with no stoplights or any roundabouts. I will normally find a lorry, or some sort of car that is going through and drive on the right of them. Anyone who has managed to get a car in this country is no doubt extremely aware of all the dangers and will be more skilled at handling the chaos of the intersections in Vietnam. They are a much larger target and the masses of motorbikes are far more likely to give way to them than to you. This is especially important if you are new to the entire process.
Number 5: Obey speed limits and wear a helmet
There don't appear to be very many rules of the road in Vietnam and for the most part, they're aren't any. However, there are two that are upheld rather strictly and they are the helmet law and speed limits. Despite the chaos of the streets, you rarely see someone traveling down the road like a cruise missile. According to taxi driving friends of mine, the speed limit laws are enforced rather strictly and I have seen multiple checkpoints for helmets. All other road activities don't seem to be enforced really at all. Plus wearing a helmet on a motorbike is just a good idea anyway. You do enjoy having a head right?
I've lived in Vietnam for year and have never had an accident. I don't really know many people that have gotten into one either. The roads look like absolute madness to anyone visiting from the west and in many ways, they are. You don't have to be afraid of it though if you just follow the above advice. It can be a bit nerve-racking at first, but once you accept the fact that they have their own thing going on here, and then just follow it, you'll be fine.