It does not mean recruiting many as possible people as friends, because in the end they might not care for you as you were just someone they known. It is up to you how you present (in business terms, sell) your personality and you as a person to others. This is mainly the hardest parts as there are some expectations people have for you and if you do not meet them, it might be "game over".
So, how do expand your social network? Well, for me and from my experience it happened a lot when I was out of the Netherlands for a whole year. Met people from all over the world and did fun things together. This leaves memorable experiences behind and we stayed in contact after. The ones who occasionally ask you how life is going, are the one who you truly and succesfully selled your personality to.
Now, the last sentence above might sound a bit like you are a product and the (going-to-be) friends are the buyers and this all is so materialistic. But thinking deeper about this subject gives me the incentive to make this comparison. And no, don't you dare think that I think about my friends like that :P not at all; I really cherish each one of them as my own family.
It is just that some fellow classmates gave me an impression that made me think about this unavoidable comparison. Some people will agree with me on this, others won't. But that is why I am sharing this with you, to open up your minds to another perspective. Open-minded people loves these kinds of things, and I am one of them. I love to hear many different opinions from people about an topic, rather than just getting opinions split in the I agree/I disagree persprective. That is why there is a saying/phrase: Always consider the other side of the story/argument. And why is that? Because you should never judge a book by its cover!