Referral card handed out at checkout for a friend's first visit

Print small cards offering a set discount on a friend's first visit, and hand one to every client at checkout with a request to pass it along. Have the front desk log which card number gets redeemed so you can thank the referring client with a small credit.

Why it works: A physical card is easy to hand to a specific friend, and tracking redemptions lets you close the loop by thanking the person who sent them.