Well, I'm not sure if that's the right way to do it. If your main site isn't getting as much traffic as you wish, there won't be enough people around to start a successful forum community. I made a forum of my own once, for my guild in a MMORPG (not the GM, but nobody else knew how), and it had around 7 regular posters. They were all regular posters in the main forum, looking for a more private place to talk, so it wasn't hard to get started with the posting. I believe that a forum should have value by itself, and exist for itself, instead of being a tool to get more traffic in a main website, so you might be using the wrong approach there.
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To build may have to be the slow and laborious task of years. To destroy can be the thoughtless act of a single day. - Winston Churchill