I thought you couldn't draft in triathlons. Maybe you can in some and can't in others... If drafting is not allowed, then I wouldn't expect the triathletes to train in pace lines much. I agree with what a few others have said here, talk it over with the others before the ride. Find out what their plans are and what they expect from you. And find out what to expect from them!
I have one more tip that I didn't see mentioned before. Don't overlap wheels with the bike in front of you. SadieKate said, "don't touch the tire in front of you." But actually keeping your wheel behind the the one in front is important. If you are overlapped and they move laterally, they may take you down. And if you go down in a pace line, EVERYONE is going to go down!
Good luck!