You can head down to the CCA Booths during the annual CCA fair held annually during Welcome Week, which enables interest groups, clubs and societies to showcase their work and talents, and recruit members.
Alternatively, you can email the respective clubs here https://www.ntu.edu.sg/CampusLife/Clubs/Documents/Web_AY1819_Clubs%20Email%20Contacts_Copy%20of%20Student%20Organisations%20List.pdf