Email the promoter or booking agency at the club to establish some sort of contact. These are the people that are in charge of all finances and ticketing for any given evening, therefore they will be able to help you with any guestlist or discounted ticketing for the event you wish to attend.
Fill out a guestlist form with your contact information if the promoter for the event has provided one. This gives the club your information for future events while allowing you to enter the club for free or a reduced price. Many promoters and clubs will have a guestlist for people interested in committing to the event far in advance.
Contact a friend or acquaintance who either works at the club or is offering a specific service on the night you wish to attend. DJs often have their own guestlist for friends who may want to attend the night of their performance, while club employees and promoters have the connections to alter the guestlist for each night.
Arrive at the club where you wish to receive guestlist advantages a few days before the event and locate a person to help you with guest services. Ask how you can help out with the event in any way in exchange for a guestlist spot. If you have audio equipment that might be useful for the night of the event, offer this gear for free admission and possible other services. If you are a photographer or have experience in any other technical field that might be useful to the club, offer these services as well. In addition to a guestlist spot, you may actually find potential work with this establishment in the future.