Bring back some old school methods with a modern twist too - upload all your contacts.
Instead of just emailing everyone inviting them to join and telling them which kind friend reccomended they join - use the birthday and home address information and send them real tangible marketing material for their birthday (+ on Anniversaries, Christmas, Easter and on any day ending with a "y").
Instead of just emailing everyone inviting them to join and telling them which kind friend reccomended they join - use the birthday and home address information and send them real tangible marketing material for their birthday (+ on Anniversaries, Christmas, Easter and on any day ending with a "y").