I moved from the UK to Spain, not knowing a single soul. I made friends by being in situations where I was in regular contact with the same diverse range of people over a period of time to the point where my face became familiar and some of them would acknowledge me. This is where casual conversation develops and can lead further, not always to friendship but this is the risk one must take.
A simple example was going to the same restaurant each day for breakfast where a couple of waiters were keen to develop their spoken English skills and would go out of their way to chat to me. This developed into friendship and breakfast soon became the highlight of my day.
Sticking to a regular routine helps a lot too because you'll soon notice other people who are always around at the same time. Maybe they have the same idea in mind, who knows, but it's a lot easier to begin a conversation with a familiar face then a strange one.
Another example was signing up for Spanish lessons. I expected to make friends with other like minded students but, actually, my teacher became a friend.
Staying in shared accommodation is another tip, it may be uncomfortable but being forced to get along with other strangers can yield the odd benefit. Dare I say it, also, co-working spaces are not an entirely bad idea if meeting new people is your goal.
I say all this as an introvert who normally finds it difficult to make friendships but I found being in alien environment helped a great deal, necessity being the mother of invention and all that.
