Most often adult games are more relaxed than junior ones (less hormones are flying about) just be firm from the start but have a smile on your face and it will rub off on the players. And finally don't worry if you are there 20 mins before KO and no body is there, they like to turn up 5 mins before the match, put the nets up, quick jog, one last fag then KO.
Just have fun and treat it as you would any other match. Good luck.