Threesomes?? AAAAHHHH

Okay, okay. So I have this friend and we always hit each other up for casual hookups or whatever. It's just normal for us. NSA sorta thing. She recently got a boyfriend and her boyfriend gave her permission to sleep with other girls so long as there are no feelings involved. She hit me up. But it was different this time. She said she was curious on the whole threesome situation and wanted to try and she wanted to know if I was interested in trying with her and her boyfriend. This is new to all of us. But I really don't want to mess anything up. Basically what i am asking is, how do threesome positions work? Like what is a good go to position because I feel like imma just mess up the whole situation and get tangled up or some shit man. I want to try but I just dont know how and I'm so scared I'm gonna embarrass myself...