How do I act around my boyfriend's friends?

To give you an idea of my age group, I'm in college.

There's a housewarming party next Friday. I know my boyfriend has a couple friends there so he's gonna wanna go. I don't know his friends too well, but I know them well enough to be invited myself.

They're always nice to me, but I feel like I don't know how to act around them. My boyfriend smokes with them occasionally, and they'll probably do that at the party too. I don't do that stuff. I drink some, but that's it.

Anyways. Every time I'm around his friends I don't know how to act. I don't know how to talk to them. I consider myself a very social person, but for some reason his friends make me very nervous and I'm a bit uncomfortable but I don't know why.

Can anyone relate or share some advice? I don't know what to do. I DO wanna go to the party, but just the invitation alone made me nervous right away. :/