Consider the types of modern dance that you have experience with or an interest in. You might be more interested in a group with a modern jazz focus than one that focuses on expressionist dance, for example. Many different types of dance, including expressionist dance, dance theater, and free dance, could fall under the broad category of modern dance.
Ask at dance schools, local universities or other dance-oriented organizations for information on modern dance groups. Many cities have contemporary dance companies that may also be able to help you locate a group. Review flyers and bulletin boards that are located in arts centers or places where contemporary dance concerts are held.
Search online for dance related forums or discussion groups. This is a great way to network with other dancers or find information on local groups. The Cyber Dance website also has a list of modern dance companies in the United States and is a good place to begin your search online.
Attend a modern dance festival or event, such as the Guelph Contemporary Dance Festival in Canada. You can learn more about the forms of modern dance and connect with other dance enthusiasts.
Start your own modern dance group with other local dancers. You'll probably want to focus on one area of modern dance such as dance theater or free style dance. Contact arts organizations or dance schools to see if they will let you rent space for your group. Put up flyers about your group or let dance instructors know that you're starting a group in order to get more people involved.
Follow the particular group's instructions for joining. Depending on the group, membership may be free or you may need to pay monthly or yearly fees. Some contemporary dance groups request you to audition, while others just expect you to show up. The best way to find out what you need to do is to contact the group itself and ask.