It's even easier if they are running the event. In this case just ask the person selling maps or giving you your start time. There is usually a person in charge of new members. They will give you all the information you need. If you do join a club then it's a good idea to get to know other members of the club.
Many clubs hold regular social evenings or training sessions.
This is a very good way of meeting people in the club. By far the best way of meeting other club members is to help at club run events. It also contains notices form some of the Dublin clubs. The Irish Independant and Examiner usually have events listed on Saturdays. The Irish Independant often has some results on Mondays.