Your experience of Asia will be amplified if you have a few skills in your possession!
The most useful skill that I found is motorbike riding. You will be able to cover A LOT more ground in no time and save a bunch of money if you rent a motorbike and use it instead of booking cars, buses and other means of transportation within town or surrounding area. For example in Hoi An you can stay either in the city center proximity or in beach proximity and both locations offer high price for accommodation. You can book something half price a bit further away and then use motorbike to rider to where you need to be. Motorbike rental is about 50-100k depending on your negotiation skills and the duration of your rent. But I found it extremely useful to have a driver license for motorbike and have good driving skills. So if getting driver license for motorbike doesn't cost you a kidney and you have time to do it - DO IT! you never know when it comes handy. Besides it is a lot of fun to ride motorbike (scooter).
Bicycle riding - second skill which many people lack. I mean that many people CAN ride a bike but they have no confidence in it and in Asia you need confidence on the road! So second skill is bicycle riding. Practice it! until you feel the confidence! Advanced skill - unicycle! try it out, learn it, you will be super-confident on a bicycle :)
Basic body language! In Vietnam many people don't speak English (not even bad English). You will need to use Google translate a lot but it is very prone to huge misunderstanding because Vietnamese is hard to machine translate. So you will need to be able to explain what you want/need in body language in many different ways. Play that game with your friends where you need to tell them movie name without speaking and they need to guess. Useful skill for big part of Asia.
In Vietnam and other SE Asia you will need to master haggling skills. You will want that because it will help you save at least half of your money when it comes to street vendors. Simple example is when you come by a shop and ask "how much is a t-shirt" the first reply is "450 000", eventually 3 minutes later you buy it for 110 000 dong! there are different ways to negotiate. I can't do it, Alena is the master of it! Alone I would probably pay 430 000 for that t-shirt and felt like a boss :)