I'm not sure whether you're wanting to dress a certain way to 'fit in' or dress a certain way to look good. If the latter, then please please avoid what the average British person wears. That's all I can say.
Best thing is to just go out there, dress in whatever clothes you like and whatever you feel comfortable in. Clothes shouldn't dictate whether you fit in or not, it's your attitude that should. And from what I can gather from this thread, you seem like a decent guy.
I could, however, point you to a few things you should not wear:
- baggy jeans
- uggs
- overcised t-shirts
- NY YANKEES caps
- long golden chains
- crocs (shoes)
- cardigan with t-shirt under
- bootcut jeans
- rifle
edit: or sweatpants