Writing what you know...?

I rarely write what I know. My story takes place in locations I have never been to. I don't try to get real detailed about the characters' surroundings, but I make sure to put in enough details to enhance the story/description. I can find out just enough by researching online if I need a street name or certain geographical points. The majority of my characters are British which means in most cases they have different words for things than we do or different ways of saying things and different speech patterns. I don't know if my portrayal of them is perfect in these respects but I try to be true to their background and heritage. Even a simple thing like one of them being in a relationship, I don't have a lot of personal knowledge to go by in how to live with someone and build a romantic relationship but I go with my own emotions and do the best I can with the rest. It's all pretty much trial and error anyway. No one knows what the hell we're doing when it comes to some relationships so I imagine the things that would be different for me if I were in a relationship as opposed to what I knew in my single life and try to figure out how the characters might work through those changes.