Don't leave your luggage backpacks exposed.
Backpack always on the front, especially bording bus/train (a crowd of 10 will work together to push, crush and steal.
There's a public bus service at every airport to the town centre ($1-$2), no need to hire a taxi (quite often the locals at the airport will lie about the bus existing).
Money, take Thai baht and your Thai ATM card.
Buy a data sim for your phone, so Google maps will work.
Try Viet coffee, it's good but strange (strong coffee + condensed milk)
Highlands coffee, do a good coffee + baguette for a couple of dollars.