Vietnam is a very safe country to visit. Violence directed toward foreigners is extremely rare and Vietnam is free from the acts of terrorism that have recently plagued many other countries. The vast majority of the population are honest, but it is always wise take take some precautions to ensure you have a trouble free holiday.
The driving in Vietnam is somewhat "interesting" to say the least. Officially driving is on the right hand side but don't expect anyone to adhere to this, or any other traffic rule. Hiring a motorcycle is not recommended especially if you have not driven in SE Asia before. But if you really must hire that bike wear sensible clothes and a crash helmet. A minor spill whilst wearing tee shirt and shorts can leave you with a nasty case of gravel rash and ruin your holiday. Head injuries, even at low speed, can be fatal.
In the major cities traffic is relatively slow and the risk of serious accident is reduced. On the major highways head on collisions are all too frequent and extreme care is required.
When crossing the road in Hanoi, Ho Chi Minh City or other busy areas walk slowly and allow the traffic to avoid you. Lots of stopping, starting and sudden movements will confuse drivers.
It is perhaps a little ironic that, whilst in Vietnam, you probably have more chance of being injured by un-detonated military ordnance left over from the Vietnam war than by an act of violence. The risk is, of course, very small but if you venture out into the countryside do not touch anything that resembles a rocket, bomb, artillery shell, mine or similar device.