How To Promote a Classified Ad Posting Website? I have solid and tested strategy.

I have been able to increase traffic by 1800% in 3 months time and given 1000+ genuine subscribers to my client's classified ad posting website. I used most of the free and other cost effective ways. My client said that he is also making some money through Adsense. But I want to improve things much faster. Is there someone who has done that previously. Please suggest!