Randomly invite people to sleep at your place. Especially if they are your friend’s friend. Not in your bed necessarily, a couch is good. I’ve met some of my favorite people this way. Random Polish hitchhikers, Danish artists, French students; I’ve walked into my own house and experienced the sense that it was a hostel. It’s immensely rewarding. Karma points, free beers, cooked meals, an extra pair of hands to setup the party. They may return the favor and you’ll have local friends across the continent. Amsterdam is a fun place to visit but it’s neither inexpensive or easy to navigate for new arrivals. Help someone out.
Another absurdly easy thing to do is accepting random invitations. When invited to take a weekend trip, volunteer at a festival, participate as a subject in a scientific study, or interview for a new website (see what I did there); just say yes. I’m still amazed at the friends made this way and the adventures we’ve undertaken. Fröccs in Budapest and beers on fake beaches. It takes time and good energy but it will be returned. There are so many beautiful people out there.