Bringing friends
Your members are the channel. Give them a reason.
Rules you set
A ladder of discounts with a ceiling. You decide how much, and how far it goes.
A gift as a link
Buy someone a class and she opens it from a link, not a code she will lose.
A leaderboard
People who come often appear on it, and the top of it earns a pass to bring someone.
Without naming anyone
Your report is counts. It is deliberately not a list of who invited whom.
Everything a studio runs
If one of the three costs you money, tell us how much.
The first conversation is questions, not a deck.