What should I call you?

A new friend introduced themself to me and used the 'family name then given name'. I've heard that if you're a foreigner, use the given name. So I wasn't sure how to address my new friend. As a foreigner that speaks Japanese, which should I use? And can I use the 'family name + given name' way of addressing people normally(if I don't already know a nick-name etc)? Thank you.

When you talk to someone, you wouldn't use the full name, right? So if you are talking to your new Japanese friend, you can say "(Family name) + san." They might ask you to call them some other way if they prefer otherwise.

If you have to introduce that new friend to someone else, and need to say the full name, you would say (if you are talking in Japanese), "Kochira wa (family name) + (given name) san desu."

There are no rules which say foreigners have to call people by, or be called by, their given name. Since you were given the full name, I agree with AK- use "family name+san" to start with.

If the person wants you to use his/ her given name, he/ she will no doubt tell you at some point.

If I read you correct he introduced himself in person, right?

If so I would ask him myself what he goes by, my two long-term japanese friends who I met using this site usually we go by our given name or a nickname, or we start a conversation while barely mentioning our name(s) after we get comfortable.

I think it all depends what you and he thinks is comfortable.