Forum posting would not be enough. You have to participate on other techniques as well like classified ads, blog commenting, article submissions, online groups, press release, social bookmarking and social networking helps.
Another method that has worked in driving quality traffic to the websites is called viral marketing. There are many methods involved in viral marketing but among the easiest would be the tell-a-friend script. This is simple but very effective tool to drive quality traffic.
You have to learn some seo techniques. you can do social bookmarking, one way link building, blog submission, article posting, directory submission, SEM and so on.