Nice question Niko,
Well, I rarely add people as friends as far I’m open to anyone. But, I receive some friendship requests from time to time. Before accepting I check the profile, what interests me at first, are the linguistic skills and the blackboard. After that I take a look at the other information, like nationality, age and gender. Because the more I know about this person, the more I know how to communicate with this eventual new friend. Thus, I can always define standards to conversations.
I prefer the one who has some of the most important qualities my opinion, like: linguistic skills, respect, culture, open-mindedness and communication skills.