NPHC groups do not rush in the same ways as Interfraternity Council or Panhellenic Council. NPHC groups typically have intake in the spring semester, and to be eligible for intake you have to have anywhere from 12 to 30 hours of completed coursework.
Specific requirements vary from organization to organization.
Check out their websites, both local and national for more specific information. Spend the fall semester researching the various NPHC organizations. Most will have tables in Jester during the first few months of school. Many organizations will also have informational meetings during this time, enabling you to learn more about all of the organizations. Look for posters publicizing their events in all of the on campus residence halls and in the Multicultural Information Center.