Assuming your site is something your users find worth inviting their friends, your best bet is to A/B test the hell out of your invitation process. What percen

Assuming your site is something your users find worth inviting their friends, your best bet is to A/B test the hell out of your invitation process. What percent of your user's send out invites? What can you do to improve this? What percent of sent invites lead the recepient to your site? What can you do to improve this? What percent of these convert to an account? What can you do to improve this? What percent of new accounts stay active? What can you do to improve this?