I invited ALL my friends, asked them to invite anyone they thought might be interested and then I offered a discount code where all you have to do is "like" my page.
I also share most of my postings on the facebook page (such as photos) to my personal profile so friends who haven't accepted (whether because they ignore requests or they haven't been on facebook in a while) see the product and maybe join the fanpage.
I also tweet the fanpage and let people know they will get a 15% off code good until the end of October if they are fans.