Difficulties in promoting an application on FaceBook

Good day. After adapting the application from the Russian social. networks in FaceBook immediately raises the question: "How to promote?". From my own little experience, it turned out the following:

• Paid advertising: For 100 clicks - 20 users, that is, only 20% of those interested in advertising reach the application itself (though this flash application is more than 600 kb, maybe it just doesn’t wait for download) and this at a cost of $ 0.5 per click
• Invitations: Only 4% accept the invitation (several accounts have been used - more than 1000 “friends”), but the average statistics for all Facebook applications is 74%
• The same application in our networks is gaining several thousand users in the first day - without ads

Dear hub users, if you have any thoughts or experience promoting Facebook, please share it (I think a lot of this will be interesting).
Ps If you suddenly submit paid advertising on FB, I advise you to first look for coupons for example on eBay.