In the beginning I had a really hard time reading English people. For example, my guy's dad has a very strong accent, and when I first met him I was like, "could you repeat that??" after practically every sentence he spoke. I must have looked like a complete idiot. It was humiliating!
(Now I understand him perfectly, thank god!)
I also wasn't sure, at first, whether or not people were joking and if I was supposed to laugh or not. But after a while I got the hang of it.
Overall, they have a fabulous sense of "humour", but they're a lot more subtle about it. They may not even smile as they're telling a joke, they'll say it totally deadpan -- you just have to think a little harder to "get it". I've found that you kind of have to keep on your toes and be careful not to look like an idiot when speaking to a Brit, or else their subtleties will fly right past you!
In America, it IS different. I feel I can just smile at people and chat away freely -- it's very easygoing-- but in England I felt a lot more shy about starting conversations because I wasn't sure what to say, or how to make small talk without being too gregarious, if you know what I mean. Like you, Mindy, I found it really hard to just be myself. :-/