Take it slow the first few times. I'm not sure if you need to prepare on the treadmill, I think the best bet is to just turn up and start doing it.
It's easy to start off too fast, because you might have a lot of energy and because others are running with you. Don't fall into that trap, just try to go at your own steady pace.
Oh and make sure you warm up and cool down thoroughly.
Remember, it's not a race.