One of the things that makes your life a great deal easier when you are visiting or living in Southeast Asia is to get accustomed to the fact that riding a motorbike taxi is just a way of life. It is extremely cheap, very accessible day or night, and much safer than trying to drive a motorbike or scooter yourself.
There are a few key tips to keep in mind when you are doing it though to make things easier for you and the driver of the bike.
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First off install an app like Grab on your phone. There are others and they vary depending on what part of the country you are in but Grab is the most widespread. With this app, you can hail a taxi from anywhere regardless of what language you speak - and I am presuming most people do not speak the local languages - and the taxi can pinpoint your location. They will also know exactly where you are going and you will know beforehand how much it is going to cost. If you are one of those people that feels the insane need to put everything on a card you can link your cards to the app and you don't even need to exchange any cash, which brings us to our next point
Have small denominations of money on you. The common newbie mistake in a lot of instances is that they will only have the notes that the ATM machine dispenses on their person. This is normally the 500,000 VND notes. It is extremely likely that the moto taxi is NOT going to have change for this and you will simply be making a problem for you and the taxi driver.
Hold on to the sides of the seat of the bike if you are a nervous-pervus. Do NOT wrap your arms around the driver as if the two of you were dating. As you might expect, hugging the driver makes them very uneasy and you could actually be making the drive dangerous by doing so, especially if you are the type of person that freaks out when faced with something they don't understand such as the way that a motorbike taxi drive is going to handle intersections. Obviously the rules all change if you are a hot woman and you might just make the driver's day :)
Enter and exit the bike on the left-hand (when standing behind the bike) side. The tailpipe is on the right-hand side and it is extremely hot. Merely briefly touching it is a fantastic way to lose a bunch of skin on your calves and I have seen many people that have lost their skin there by making this terrible mistake.
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unless the bike is strangely and unnecessarily modified, the tailpipe is always on the right
Sit in one place and don't bob around to take photos or whatever: Doing so throws off the balance of the bike and can make it difficult to control. I know this from experience of driving bikes for years. When the passenger is mucking about behind you the weight displacement shifts as well and this makes the bike much more difficult to control.
RELAX! A ton of people get really nervous about riding on a moto taxi because they do tend to drive pretty fast and bob and weave around traffic. After years of experience I try to look at this situation from a statistical standpoint: This driver does this for a living all day, every day; and he isn't dead. The chances of a crash happening when you are on the bike are extremely small. By freaking out, you only make the ride more dangerous.
If your driver was really good IE: Polite/on time / didn't drive like a lunatic. Leave them a 5-star review on the Grab app and maybe tip them a little bit. You don't need to go crazy but it might surprise you how much a tip of 20-50 cents actually makes their day!
Riding a motorbike taxi in most SE Asian countries will save you a ton of money over getting taxi cars. They are also significantly faster than cars on short distances not involving a highway. Once you embrace the process it will simply become a part of your life that you no longer mind doing and eventually you will become like one of the guys in the top photo that are just at ease and looking at your phone during the trip. It seems dangerous to the uninitiated but in my years of living here I have never heard of anyone crashing on these trips. In that same time I know plenty of people that have crashed their own bikes.