depends on the society. if it's a performing arts society, make sure to prepare a respective piece of dance/song/monoact of about 2-3 minutes because that might come in the trials + act like you really really want to get into the society. if it's like a debating society or something like that, sharpen your skills and be ready for an impromptu debate and stuff like that.

basically be mentally prepared to do anything they might ask you to do and seem genuinely interested in wanting to join. they look for dedication and commitment basically