how to keep yourself safe from scams, thieves. how much money to bring, in what form, in what currency, what language(s) to learn/speak even if just basic phrases, where to sleep, where to eat, what to do, when to do it, when to go visit, when not to do things, what not to do, what you should do, how to do it, local laws on what is legal and illegal, how to travel/get around town/cities, the way to respect the locals, their religion(s), culture, etc, etc
What sort of place they are going to. For example urban, rural, modern or old. It needs to correspond to their personal tastes. They need to know what to see when they get to their destination, by researching on the internet or buying a guide book. They need to know how to get to their destination - by train or air or sea.
They need to know how to travel around their destination. What is available in terms of local public transport or whether to hire a car
If they don't then not only could they face issue at immigration, they are also going to be wasting lots of time and missing lots of things if they are allowed in
Stuff.
everything. don't want any surprises.
