For me it's simple. Get a really good tour, leak free, and convert the traffic that I send to you. It's not easy, I know. But... if I hear from a fellow webmaster that a site is converting at under 1:400 regularly for them, I will sign up and send traffic. It has to be in ICQ or something private like that, and from someone I trust. In short, word of mouth and viral marketing
and as program owner all you can do about it is -
1. Make sure your site is really really good and converts very well.
2. Never shave, have leaks and what not. Give your webmasters full credit and get them to see good ratios.
3. Give nice referral bonuses/percentages for webmaster referral.
I would prefer to go with 50/50 on a very well converting site. Then give 10% extra for referring affiliates. Now, if your site is converting extremely well, people will get the word around...