Dynamic Referral scheme
I run an incentive in our box, and its helped massively. we've grown by 40 members this way.. thats nearly 50%!!
For every new member an existing member brings in (that graduates from the on-ramo) they (the existing member) get 5% off their membership for the lifetime of the new member.
this aids ember retention as the existing member has vested interest,and it rally boosts numbers. its a very powerful reward structure, more so than simple on-off .
it would be even better if the % discount was based on the membership of the NEW member.