1. Check the weather forecasts in those cities you are visiting.
This is very important, you do not want to go to a place with a nice beach and end up stuck in the close vicinity of your hotel because it rains the whole freaking day. To make it worse, we had the view of the sea/beach from our hotel room. It's a horrible thing to see something so beautiful everyday but not being able to touch it (the same way I feel about most women I meet)
2. Don't bother bringing too many clothes, toiletries.
T-shirts and shorts are really cheap as hell (around 2 dollars), so don't bother bringing too many of your own clothes and adding more weight to your backpack. Especially heavy clothes like jeans and jackets.
3. Don't change your money in Singapore !!!
Our local moneylenders' rates suck so much, I changed 350 in Singapore at a rate of 1 Sing dollar for 8400 dong, in Vietnam it was 9400 dong. Hell of a difference, it is. When you are soliciting services from young hot Vietnamese women on the street, every extra dollar counts, take it from me.
4. Use a travel guide book.
Get one of those guidebooks and research on the places to visit, sleep, eat. I used footprint Vietnam guide that we got from the library, it was pretty good , very detailed and also gives you the estimated cost for the attractions/transport so you don't get ripped off by tour operators. And believe me, some will try and rip you off, especially the cyclo drivers. Make sure you confirm prices before you do anything, and ask if there is any other costs for the whole trip.
5. Know how to ride a motorbike/bicycle.
Motorbike rentals are pretty cheap (I think it was 10000 dong for a day), so its a good option for less busy towns like Nha Trang and Dalat. You can get a bicycle for even cheaper, I think like 2000 dong. Beats the hell out of walking.
6. Don't bother about vehicles when you cross the road in Ho Chin Minh/Saigon
Seriously. In Ho Chin Minh it's the responsibility of the motorcyclists to avoid you rather than the other way around. Yes it sounds crazy but its true. But please take note that I am pretty sure this only applies for bicycles and motorbikes, I haven't tried it with cars or buses, but you are welcome to try and feedback to me.
7. Don't trust people's answers when you ask them how long a train/night bus journey takes.
The hotel receptionist informed us that it takes 5 hours from Saigon to Nha Trang by train, and another told us it was 4 from Nha Trang to Dalat. We ended up taking 7 and 6 hours respectively. It is safer to ask the train or bus operator what time you will reach your destination and calculate the time yourselves.
That's about it I guess. Yes some of it might seem like common sense to you, but please do note that it was my first backpacking trip, and I had lots of distractions and suffering from really bad cramps before the trips....fine I am a stupid dumbass for not checking the weather,that's what you wanna hear right?? You happy now?? Makes you feel good to put down others doesn't it?