I work for a large international telecommunications company, and have colleagues all over the globe. Though I am located in the US, I deal with people in other countries every day on every project. There are a few things to keep in mind, regardless of where in the world your cubicle is located, when you're dealing with co-workers, customers, or suppliers in other parts of the world.
First, something as basic as time zones can be a challenge. If you have a colleague in Berlin, and a customer in California, it can be tough to find a time convenient for both to hold a conference call. You need to keep those time zones in mind any time you are trying to get people together. Second, there will be language issues. English is the language of global business, but there will be folks in your dealings that have strong accents or a lack of English mastery. Show patience, be kind, ask for clarification when necessary, and re-state what you heard to ensure you understand what is being asked. Third, be aware of cultural differences. In some cultures, it is considered rude to tell a person of a higher level anything negative, whereas in the US we tend to be much more open regardless of a person's title. So you may ask someone to give an honest opinion, but they will couch their response so as not to offend you. This can change as you build a relationship, but until you get to that point it can be frustrating.
These ideas are more around the areas of interpersonal skills. Keep in mind there are also a myriad of legal, regulatory, and statutory differences between countries - those are things your schooling and eventual employer will help you understand and master. Plus, there is the whole part of the equation related to actually living in another country - there are many good resources on line, as well as good old-fashioned books on the topic. Good luck!